basic plot of the next game: your parents died and you end up living with your rich uncle(your mother's brother iirc) who literally gives you the harry potter treatment(your cousin even points this out) and his daughter who adores you from the start. your uncle has you work and train as your cousin's bodyguard until the day he can kick you out. so life carries on like this this one day one of your cousin's two friends decided she wants to check out a urban legend and gets isekai'd by shadow monsters(friend #1) with your cousin chasing after her leaving you and the other friend(#2) traumatized by the experience(also your uncle beats you up because of this)
jump a few years to present day and after getting beat up by a girl(classmate #1) it's shown that your cousin's friend(#2) is now your bully. it's at this time that your whole school get isekai'd(though your unaware of this at this time and have class as normal) and one of the girls(classmate 2) your class passes out so you and classmate 1 take her to the nurses office after which classmate 1 is attacked by a boy with pink eyes(infected) you save her eventually finding your teacher and other classmates who where being protected by your cousin, friend 1 and a fairy. both you and friend 2 are shocked that the two of them haven't aged and their don't believe the two of you are you.
you now learn a few things
for your cousin and friend 1 it's only been a couple of months instead of a few years since they got isekai'd
you can acquire a energy known as mana and use it as currency to buy weapons, supplies and a return ticket sends you back to your world
you get a set amount of mana as a "login bonus"
you can also take other peoples mana
you can enslave someone by taking all their mana(the mc will never do that though)
a man's mana is stored in their balls and mixes with semen guys lose a lot of mana if the masturbate
everyone who comes to this world gets powers (your cousin's makes doors to a pocket dimension that is a replica of her home and yours is status anomaly immunity)
if you enslave someone you also take their power
everything changed when the person with the virus power came to this world
infected can only spread the virus to people of the opposing gender
most male infected are basically horny zombies
female infected tend to be more lucid but tend to instinctually seek out uninfected males
according to the fairy killing the person with the virus power should put everything back to normal