First of all, make sure you have Kanji available as a party member. Make sure that he's either in the first floor of the practice building, or in front of his family's shop---this means, make sure it's a Wednesday, Thursday, or Saturday without rain. A final requirement I found is that you need to have no one in need of rescuing in the TV world, or else the students will be too busy with gossip.
A girl called "Female Student" should be in the 2nd floor of the school, directly in front of the main staircase. Talk to her, and hear her claim that Kanji has been bullying.
Now, go find Kanji and talk to him about the matter. You'll spend the afternoon, and build the first level of his social rank.