WARNING! HEAVY SPOILER!
The school was build above Dungeon
MC is like muscle brain with strange moral judgement
MC is described as person with HEAVY KILLING INTENT but of course it's false alarm
The first friend (Seiji) telling him what kind of school this is start with inviting two other female student and they have consensual sex, so he got impression that everyone in this school is like this (he misunderstood)
So, sex or rape that happen nearby or in front of him is like normal greeting or just student deepening their bond, he "think" it's all consensual but of course it's not
If you're curious about the teacher, she has Princess Class that cannot refuse sex related order
Lots of rape happen in this school, especially in the first year, in 2nd year it's not rape anymore but accepting fate, in the 3rd year their presence is slowly fading and only lives for sex. They either strong enough to become sex slave or sacrificed to the dungeon (lost case)
If you curious why this school become like this because very old group of chairman extending their life using elixir and to keep dungeon keep running, they sacrificed useless students (mostly female) and call it as Lost Case
Most dungeon must be conquered especially the Raid Type, the longer dungeon exist the dangerous they become except for a few safe dungeon. If dungeon conquered, it disappear and later a new dungeon will appear
About NTR, worry not, MC keep his harem safe. There is one NTR happen to MC in the beginning but it was "What If" scenario, so yeah it's not count. MC grow fast, so he can protect his harem
Most of the students here are degenerate due the influence of dungeon, nice person like MC is actually very rare. The other type is gentleman, they rape but treat the girl good (they're popular among girls), but sadly they're quite weak so their girls often kidnapped by senpai. The rest are degenerate, trash of society and you can divide them by 2 group, Strong and weak. Strong prey monster and kidnap girls meanwhile weak afraid of monster and instead kill other male to get the girls. This will only happen in the dungeon because death inside dungeon is just log out from dungeon and you lost memory of what was happen inside
The worst about this series is how blockhead the MC is, also he is more like if my girl like other guy she can have sex with that guy
BTW, one of the main girl will become yandere and later will write BL doujin about MC and Seiji, surprisingly it become very popular among girls
