HOW
i did what another reply said
Change the player's gender to she/her, join the Art club, when u introduce yourself say that u like drawing, painting, and visual art , always enter her club on breaks. Then on a certain club meeting, Japan would ask you what's your favourite type of game? Select the answer "visual novels" and she will say she's working on a dating sim game,, You'll have to agree to help her make it.
So yeah just agree to whatever Japan is saying and you will get the ending ;D