Saku Tatsuhiko

Saku Tatsuhiko (佐久 辰彦) is a minor character introduced in Toaru Majutsu no Index. He is the leader of BLOCK. On October 9 he tried to lead the faction from the Dark Side of Academy City along with 5,000 mercenaries from the outside of the city as part of their plan to attack Aleister Crowley. His plans are later thwarted by the efforts of GROUP.

Appearance
He is a large man who is constantly being described in the narrative as "bear-like." He wears his hair as a crew cut.

Personality
Tatsuhiko is a man who is serious in his goals. He is cold to those who have become useless to him such as Tetsumou and is unforgiving towards traitors such as his subordinate Etzali framed as a traitor. He has an extreme hatred for Aleister Crowley, so much so that he is willing to put people in danger even if doing so is unneeded.

Background
Not much is known about Tatsuhiko prior to October 9, though it is known that he is acquainted with Teshio Megumi's past with Anti-Skill. As the leader of BLOCK, his primary duty is to keep an eye on the level of cooperation from friendly institutions outside of Academy City. It is likely this experience with the outside world that allowed him to hire 5,000 mercenaries later on.

As he and the other members have an animosity against Aleister Crowley and his control, they saw that they can challenge his will after the events of the 0930 incident. He successfully manage to take control of the organization including its subordinate group from the BLOCK liaison and somehow managed to hire 5,000 mercenaries from the outside of Academy City. Their plan was to storm the Reformatory using the mercenaries and take hostage of Musujime Awaki's comrades that have been kept there as a leverage to force her to cooperate with them regarding the secrets of the Windowless Building, Aleister Crowley's base, which would then, if successful, allow them to execute their masterstroke, transport a Synchronous Multilayer Bomb into the building itself and assassinating him.

Battle Royale Arc
With the Powered Suits busy over at Avignon, BLOCK intended to do their move on October 9, Academy City's Independence Day. However, they later discover that SCHOOL is doing their own moves on the same day as well, an assassination on Oyafune Monaka. This forces them to rethink their plans and found it fit to use SCHOOL's attempt for their own plans. Apparently discovering that Management, a person who has assisted in SCHOOL for their assassination, has been caught by GROUP and are on track in discovering SCHOOL's plans, BLOCK sends word to SCHOOL of Management's current status. In order destroy the evidence regarding SCHOOL's plans, BLOCK has a group lead by Yamate to attack Management's apartment in Family Side. SCHOOL later kills Management, and though their assassination attempt on Monaka was thwarted by GROUP in spite of BLOCK's efforts to destroy evidence, it was but a means to an end as their true intentions have been realized.

Yamate and his group later return to BLOCK's base in District 10 near the Reformatory. Unbeknownst to Tatsuhiko, there is a spanner in the works, as Etzali has killed Yamate during the operation and has taken his appearance. Disguised as Yamate and suddenly being in BLOCK's base, Etzali is anxious. Seeing this, Megumi asks what's the matter, to which Etzali says it's nothing. Megumi then says that he should pull himself together as the plan's success depends on his power. Tatsuhiko then tells Megumi that SCHOOL has made their moved and laments on the fact despite giving them the information regarding Management. Megumi then says that it won't be easy outwitting Academy City but says that's also a reason why they can't give up. She then asks about the Man on the Phone, to which Tatsuhiko says that both he and the Hound Dogs are of no concern. After Etzali's ponders on how the subordinates are supporting an actual rebellion, Tatsuhiko then orders Tetsumou to use her Skill Polygraph to make sure there isn't a traitor among them, their usual safety check. Etzali becomes surprised, though manages to hide it. He quickly conconts his plan, playing around with hand cream before his turn and spiked it with a small quantity of liquid explosives. After analyzing Saku and Teshio Megumi, the latter's past disturbing her enough for Megumi to advise to stop reading her mind, it was Yamate's turn. Before Tetsumou could get to him, Etzali pretended to lose his grip on the hand cream container, forcing a minor grunt to pick it up for him.

Etzali goes to it and has him get analyzed by Tetsumou first instead of him, rubbing the dangerous explosive on his hand. As Tetsumou touches his hand to read his mind, their hands suddenly burst into flames, and she loses a few fingers of her right hand. The shock and blood loss then renders her unconscious, which prompts the grunt to reach for the first aid kit, but Tatsuhiko executes the grunt despite his pleas, believing him to be the traitor inside their group all along. Noticing that Tetsumou could no longer function as a polygraph, Saku shows no interest in her condition, saying that there isn't any time to "find a replacement" and instructed some of his men to take care of her body. With that done, Tatsuhiko goes to his laptop and begins the next phase of their plan.

Thus BLOCK begins hacking the Virus Isolation Center and spread the viruses through the External Connection Terminals and at the same time hack Hikoboshi II's satellite control center as so they can use the satellite in order to split the forces that would be sent out to deal with it. BLOCK's main goal with the hacking however was to take down the surveillance system that Hikoboshi II satellite had and deliberately spread false information of using its large caliber ground-attack laser to attack District 13.

Later, Megumi asks if Tatsuhiko has done it, to which he says that he did so. He says that he used the Virus Isolation Center as a dummy while District 23, where the antenna for Hikoboshi II was located, was understaffed. He then tells that what they have done is the first step in the world Aleister is in. As Etzali ponders what to do, Megumi reports on how something has happened in Distrct 23. Here she states that a number of Anti-Skills have been defeated though none of them were killed or had fatal injuries. She continues that from there at high speed the offender went to the antenna. Tatsuhiko asks which organization is behind it, presuming that it may be MEMBER. Megumi then says that it is GROUP's doing and it may have been it's most recent member, the Level 5 known as Accelerator. Etzali sees a photo of Accelerator on Megumi's monitor, and thinks it was taken in District 23 by a member of BLOCK's subordinate organization. At first Etzali becomes nervous with BLOCK discovering Accelerator, but then realizes that BLOCK may not be able to snipe or attack from the distance where the photo was taken. Megumi then asks what they should do, to which Tatsuhiko says that it is obvious and that is pray for success. At first Etzali doesn't understand his reply, but then realizes something, they were trying to take down Academy City's surveillance capabilities. Tatsuhiko says that a frontal assault on District 23 would have been difficult for them, but their current situation wouldn't have occurred if the antenna wasn't destroyed first, as such they needed the likes of those who are powerful but stupid to do the job for them. Megumi says that they may have overthought as Accelerator has already reached the antenna. Tatsuhiko says that the higher-ups must've opened up a path for him as Accelerator should've been already attacked by HsAFH-11 helicopters already, though it doesn't matter since Accelerator can defeat all them. Megumi then asks if they should really use the mercenaries waiting outside the outer wall of District 11. Tatsuhiko then chastises her for having second thoughts of having unrelated people getting wrapped up in their plans. With that, Tatsuhiko ends the hacking done by his laptop and turned it off. He then tells them that they should go now as 5,000 mercenaries are waiting for them outside.

BLOCK arrives in District 11 near the outer wall of the city. With the city's surveillance down, BLOCK is waiting for an opportune time to make their move with allowing their mercenaries in. Etzali is aware of this, though he does not know if the other members of GROUP or even the higher-ups know of this. Etzali wonders what BLOCK's goal is with the mercenaries is, not knowing what they're going to attack with such a massive amount of forces. Megumi who stood nearby asks Yamate believing him to be nervous about their big plan, the person Etzali is disguised as, if he is worried, to which Etzali responds in the negative. Tatsuhiko then complains about the Security robots still moving around in his impatience. Megumi asks if that is a problem, though he says that they are unarmed, and that the mercenaries can get over the wall if they time it right. Etzali then asks why they aren't armed, to which Tatsuhiko explains to him the reason. Basically, what the security robots do is not shoot at targets but use a special communication line to sound an alarm in District 23. This would then mobilize unmanned attack helicopters HsAFH-11, the Six Wings, to attack the intruders. Tatsuhiko then looks at his watch and determines that in 10 minutes the rotation of security robots will begin to recharge, allowing for a 20 to 30 minute gap in the security. As communications with Hikoboshi II which usually filled in the gaps in the security in this rotation, this gives the mercenaries BLOCK hired some time to enter into Academy City. Tatsuhiko then orders to prepare vehicles for the 5,000 mercenaries that are coming.

Tatsuhiko is unaware of Etzali's thoughts as he radios and instructs the mercenaries outside through a radio. Etzali decided to attack now as he had no way to contact GROUP. He later finds a nearby parking garage and takes out his Spear of Tlahuizcalpantecuhtli to destroy it. Tatsuhiko and Megumi witnesses this inexplicable action by their comrade, and as they have no knowledge in magic they merely stared at him. However, shock dawns upon them as they see him running towards the parking garage as it collapses. As Tatsuhiko yells at him, Etzali is fired at by BLOCK and the others. However, he was protected by the collapsing parking garage and then used his obsidian knife to make a hole on the ground to the sewers, allowing him to escape Tatsuhiko's wrath. Shortly after, an emergency signal is sent to District 23's Air Superiority Preservation Control Center, and due to the surveillance satellite being out special defense conditions, allowing him to immediately mobilize the Six Wings attack helicopters to  District 11.

Tatsuhiko curses Yamate as chaos falls upon them. The HsAFH-11 unmanned attack helicopters with their Flame Crash bullets easily slaughter thousands of BLOCK's mercenaries. Both Tatsuhiko and Megumi are in cover as the attack takes place. The latter then yells to Tatsuhiko that they need to give on the mercenaries as traveling in large numbers while being watched would make them sitting ducks. Tatsuhiko says that if the abandon the 5,000 mercenaries, then all their efforts in getting them would be for naught. However, Megumi says that the mercenaries may have already believed that BLOCK betrayed them. Furthermore, she says that the ones left outside will not come anymore. Megumi suggests that they need to retrieve those that are inside and retreat. Still angered by Yamate's (Etzali) betrayal, Tatsuhiko curses him and promises to kill him.

Tatsuhiko acquiesces to Megumi's suggestion. He retrieves about 100 mercenaries and takes them to Reformatory for the next phase of their plan. Tatsuhiko and his mercenaries later manage to take control of the Reformatory in their attack, allowing them to go in deeper in its bowels to find Musujime Awaki's comrades. They come upon MEMBER operative Xochitl, though since she was only waiting for Etzali she only attacked those who tried to attack her.

When Tsuchimikado Motoharu and Musujime Awaki were able to enter deeper into the Reformatory, Saku Tatsuhiko with Teshio Megumi were already before a solitary confinement cell trying to break the metal doors open with explosives. Seeing them, Tatsuhiko says that they must be from GROUP. Awaki didn't act immediately due to the effects of the anti-esper devices including the AIM Jammer in the facility. Motoharu tries to fire a gun on Tatsuhiko, but before he could do so, he sticks a wire into the door and tells them that he is using a plastic explosive and an electric fuse. Megumi then shouts at him, but Saku says that they must use the hostage behind that metal door. After removing his hand from the bomb he then takes out a detonation device. He says that the amount of explosives he has set has been adjusted, and the blast will all go into the door. He laments on how though it is easy to destroy the door, since the two from GROUP arrived the safety of the hostage cannot be guaranteed as he couldn't finish setting it up. Suddenly, a loud explosion rang out in that hallway where they gathered due to an enraged Awaki using having teleported a few objects into the wall. Tatsuhiko smiles, recognizing that they are before the Move Point, the very reason why they attacked the Reformatory in the first place. Tatsuhiko is glad that he has the hostage and the person to negotiate with before them. Awaki then asks if what would happen if she refuses their demands. However, Tatsuhiko is confident that she won't refuse, knowing about the AIM Jammer and the anti-esper devices in the facility. This silences Awaki. Tatsuhiko then asks if they have learned anything fromt the 0930 Incident. He says that because of that incident they have learned that Aleister Crowley doesn't always have control and that there are ways to escape his grasp. Awaki replies however that they are also trampling others in the process, and compares it to the massacres of the Age of Exploration. But Tatsuhiko says that what is he wishing for, a paradise or heaven that he doesn't have, is something all humans do. Motoharu is hesitant on firing Tatsuhiko in the fear that the detonation device might accidentally trigger an explosion, while Awaki is too enraged to do anything. Seeing the impasse, Megumi tells Tatsuhiko that using the hostage won't help. Tatsuhiko is confused by her words, saying that the hostage's value just went up. Megumi explains on how the hostages were supposed to draw Move Point, Awaki, into a negotiation because BLOCK didn't know where she was, but now since she is right in front of them, the hostage and the bomb is not needed any longer. She then tells Tatsuhiko that since from the beginning she was against what they were doing, and that she only agreed to take hostages as it was absolutely necessary. Tatsuhiko then states that they cannot do that as they have 38 hostages now, a big opportunity that they cannot waste. He asks her if she started feeling empathy for the kids inside the cell due to her history in Anti-Skill. Megumi tries to reply but Tatsuhiko continues his tirade against her, saying that he will kill Aleister and that if she gets in the way he will kill her too. Before he can finish his sentence however, Megumi punches him. Her punch was enough to knock him unconscious and make him foam in the mouth.

Tatsuhiko was unconscious throughout Megumi's battle against Awaki. Considering the situation in which he was taken out, it is quite likely that he was apprehended afterwards.

Quotes

 * (From volume 15): "This is the first step towards saying goodbye to this shitty world where every little thing is permeated in the stench of Aleister."
 * (To Megumi, ibid): "Don’t get in my way!! I’m going to kill that bastard Aleister!! This is the first step. It can’t all end here!! I can’t waste all my time here. If you get in way, I’ll kill you too, Teshio!!"