Daihaseisai

Daihaseisai (大覇星祭 (だいはせいさい)) is a city-wide interschool sporting competition that takes place September 19 through September 25 in Academy City.

Event
Daihaseisai is a famous Academy City competition where students from various schools compete against other schools in numerous athletic events. During the week of the competition, Academy City is packed with tourists and the students' parents. It's noted that finding somewhere to eat is more difficult than getting something to eat, and even the restaurant Touma, Index, Mikoto, and their parents eat at doesn't even care that they brought their own food in. There are a numerous competitions, though only a few are delved into, as Touma spends the majority of the novel chasing down a magician. Of the few events covered, some are Ball Tossing, Ball Rolling and Wrench Pole matches, with the goal of the wrench pole match being to knock over the opponents' respective pole and guard their own.

Participants are encouraged to use their abilities during the matches, which is why the high-class schools like Tokiwadai excel during it. In some cases where events are held in the general public, abilities past a certain threshold are forbidden in case they harm the citizens, like when Mikoto was in the 'borrowing-items race' she could not use her powers as it was too dangerous, even if she restrain herself. These restrictions don't apply in other matches where it is only school versus school.

According to details in a pamphlet given to students, the main purpose of the festival is to observe large-scale interference between Power Users.

Plot
Daihaseisai takes place on September 19 during volumes 9 and 10. In the volume 9 prologue, Touma makes a bet with Mikoto that his school will beat hers, which leads into the premise of volume 12. During the event, Touma doesn't actually participate much, as the majority the 19th is spent chasing after Oriana Thompson along with Tsuchimikado Motoharu and Stiyl Magnus. While they pursue Oriana, they try to learn the real goal of Oriana and Lidvia Lorenzetti. Along the way, Himegami Aisa is hospitalized due to a misjudgment by Oriana, Fukiyose Seiri is also hospitalized by touching one of Oriana's traps, and Motoharu is injured several times. After pursuing Oriana until dusk, Touma manages to defeat her, but it turns out his efforts were futile, as not only did Oriana not have the relic to thwart their plan, the magicians' plan wasn't going to succeed since the beginning. In the end, Touma is hospitalized from the injured caused by Oriana, and two days later, he was alright, but got into all sorts of unfortunate events for the rest of Daihaseisai, finally winning first prize in a lucky number contest on the last day of Daihaseisai, which earned him a trip for two to Italy.