Ichihanaransai

The Ichihanaran-sai (一端覧祭) is a cultural festival-like event that takes place across the entirety of Academy City in November. It is considered the world's largest cultural festival.

Background
The Ichihanaransai has been mentioned several times but not many specific details about it are currently known. It is apparently a cultural festival-like event that takes place across the entirety of Academy City. It is held in November and also doubles as an open campus time. Money is given to each of the schools of the city to prepare for it. According to Fukiyose Seiri it is the largest Cultural Festival in the world.

Orsola Aquinas Rescue Arc
While talking to Index, Tsuchimikado Maika mentions the Ichihanaransai as one of the many activities that occurs during the second semester in Academy City.

Skill-Out Uprising
When in class, Kamijou Touma overhears a girl mention that the Ichihanaransai might be affected by the possibility of war occurring. A little bit later someone else mentions that the class trying to decide where to go to eat feels like preparations for the Ichihanaransai.

Volume 14
After running into Kamijou Touma, talking with him, and him leaving, Misaka Mikoto remembered that she originally wanted to talk to him about the Ichihanaransai and get him to promise to go around it with her. Due to how the Daihaseisai turned out she wants to hurry up and take measures to ensure the success of the Ichihanaransai. She figures she should try to reign in Touma in the beginning since over half of the Daihaseisai was trouble related to him. However, Mikoto ends up not talking to him about it as he was led away by Oyafune Monaka and she could not find him again or get a hold of him with her phone.

Volume 17
It is mentioned that the preparations for the Ichihanaransai were slowly beginning in small waves and that as the midterm exams had been canceled the students were felt they had more spare effort to put towards the festival. Aogami Pierce mentions how the high school Ichihanaransai seems different from when they were in middle school as they get a much bigger budget and can do more things. Tsuchimikado Motoharu responds by saying that Academy City is having the festival double as an open campus time so they are giving more money to places that aren’t very proactive. Thus they have a bigger budget as their school is pretty mediocre and doesn’t have much of a burning desire or anything to be proactive about it. Fukiyose Seiri, however, was shown to be extremely excited about the upcoming festival. When Tsukuyomi Komoe arrives in the classroom she announces that they are going to be deciding everyone's role in the Ichihanaransai.