Besides kasumi you have to fuck her when she goes to the toilet on the 1st floor. There are 2 triggers. Kasumi as site assistant and fuck azusa when entering the 1st floor toilet. try downloading and reading this pdf carefully. Things in the game, are all listed there.
https://www.mediafire.com/folder/66f5v3rhabzcr/LAGS+Games+Guides+with+Images#66f...