What this game actually needs is the Netorase route, how it would unlock?
-Have one of the girls like you enough to start handjobs
-Have John corrupt her enough to have vaginal sex
When checking on her through the door`s keyhole kazuma will notice the door is unlocked and there will be a prompt:
-Remain in denial
-Open the door (starts Netorase route)
The girl will be startled and try to make excuses, Kazuma will interrupt her and say he actually thinks it is kinda hot, John will pick up on it and say "hahaha boy maybe we can be friends after all" and so the Netorase begins, each girl will have a different flavor of Netorase:
Aqua is for the masochists, she will flaunt her relationship with John, call Kazuma a tiny dicked quickshot in public, use Kazuma as a chair while John fucks her face and only agree to kiss Kazuma after John cummed in her mouth.
Megumin is the loving Netorase route, she only has gentle and loving words for you while he is being bred by John, she asks you to hold her hand while she is fucked, says how good is to receive Kazuma's love and John's dick at the same time, when going on dates with her she disappears during the date and comes back with a hair on her cheek, she kisses Kazuma and he smells cum in her mouth.
Lalatina loses all control and goes full nympho, her sense of shame is totally broken and now sex for her is as natural as breathing, when taking her out in the outskirts there will be bestiality scenes where she fucks monsters and asks Kazuma to wait and watch because it is too dangerous to get close while she is "fighting"
Once the girls have succumbed to pleasure you will no longer be blocked from interacting with them, you can open the door and talk to them, but instead of the "spend time with them" option there will be "lets go look for john" since he will be fucking one of the other girls, this will result in a event where 2 or even all three of the girls get fucked and you watch. There could be some other NTR events here like Lalatina asking to "go out "slay" monsters" where you can have more NTR without John around.