Go to the school and talk to the girl in front of Classroom 1-1. she will tell you to find her friend who is in the practice building f1. Speak with her to find out that naoto had an arguement with a fellow cop. speak to him just for him to tell you to f*** off so you run and cry to chie who tells you to be a man and to tell him your a friend of naoto's just for him to say that naoto's acting like a child and that you must talk to another cop. (Tuesdays, Thursdays and Saturdays are the days he is at district south). Then talk to a cop at the north side of the shopping district on Monday, Wednesday or Fridays. Then just piece to facts together.

long story short run through the dungeon till floor 6 the search for chests one should have the "researcher's card" in. make your way back up to floor 4 where straight from the entrance on the right should be a locked door which only opens if you have that card. make your way through the ne section to the mini boss. beat the mini boss to get the chest behind it which has the "leader's card" make your way all the way to the bottom and fight the boss! thats pretty much it