BJ? Goes to aki's (umm, archdemon, which you can meet her at very beginning of game). next right of her place is a candy gacha? just goes to it, buy a candy (around 4500 yen). unfortunately, it is random from green, blue, pink (you need is pink). then in dark, treat her a drink then treat her pink candy (if you have candy, after choose drink, it will ask you if you want to have a candy too!). Best wish, my friends.