-Only 16 chapters and he already have a harem of 3.

No. He only has FMC and the Maid. These are the only girls he had acknowledged after chapter 70. The other girls fall in love with the MC but MC doesn't reciprocate their feelings and the FMC ruthlessly protects her position as main wife.

-Immediately switch personality when he possesses the villain. No one bats an eye

No. This is a recurring point in the entire series. They didn't ask him at the beginning since they are mindful of the MC position as the son of a Duke, but from time to time they ask him if there is anything wrong.

It has even gotten to the point where throughout the novel, the MC's associates (FMC, Maid, Butler, Teacher, Friends) meet up and discuss whats going on with the MC.

They are even sometimes on the mark when they think the MC is different from the guy they once knew.

-SA'ed a girl (og villain's action), said sorry (our mc), girl says aight I guess you're not bad. Let me be part of your harem. Let me just forget it never happened because why not

This is a wrong. The SA didn't happen in the Main Story. In the OG/Game story, what happened was OG villain first met with OG FMC/Heroine who invited her to dance with him at the ball and during the ball he brought her to his room and did the SA.

In the Main Story, MC as woke up as the Villain around the time after he asked her to the dance and before Dance itself so the SA did not happen yet. So MC went on to just dance with the FMC instead which led her to fall in love with him and get engaged.

-Change personality to a doormat beta MC (you know, the regular JP MC) who everyone goes "I have to protect him with my life and not question literally anything he does"

His personality in the first volume is chaotic since his old personality (The original Weiss) is influencing MC. Which is why at one moment he acts edgy and the next moment polite. But by the end of Volume 1. His personality settles down and he becomes a Male Tsundere.

He isnt a pushover at all and is rather cold and unfriendly but he is squarely a good person capable of altruism if the situation calls for it. And he greatly values his friends and family.

-Change personality to a doormat beta MC (you know, the regular JP MC) who everyone goes "I have to protect him with my life and not question literally anything he does"

His personality in the first volume is chaotic since his old personality (The original Weiss) is influencing MC. Which is why at one moment he acts edgy and the next moment polite. But by the end of Volume 1. His personality settles down and he becomes a Male Tsundere.

The good thing is this series will get a Light Novel soon so hopefully they can improve stuff.

has sex

who has a busted copy ability that allows him to copy any spell he sees.

has s*x with the Heroine and Maid. That alone should at least give it at least 3 stars

Weiss

-The MC in the story and an antagonist in the game. In the game he was kicked out of school, disgraced and became a servant of the Demon Lord where he was killed by him.

-In the story, he works his ass off to avoid that fate the moment he woke up as Weiss.

-Currently engaged to Cynthia who is the FMC and was the Heroine in the game and the only one he loves so far.

-Unaware of the harem growing around which annoys Cynthia a bit

-Has a rivalry with the Hero and clashes with him in beliefs but respects him and his power nonetheless and deep down considers him a friend.

-Comes off as a bad guy but he's basically a tsundere and everybody slowly realizes that and warms up to him as the story progresses.

Cynthia

-The FMC in the story was the Heroine in the game

-Was the Hero Allan's love interest in game after his Childhood Friend Shari died during school.

-Hated Weiss in the game as the Heroine as in the game he first tried to play nice to her and then tried to r*pe her during a dance party, but in the story MC woke up as Weiss before the r*pe attempt

-MC aimed to at least be in good with her and initially thought she would end up with the Hero, but MC went overboard and she ended up falling in love with him instead and got engaged.

-Incredibly loyal to Weiss and its heavily implied they have s*x more often than not (She is seen talking to him while naked on his bed in his room and sometimes has threesomes with the maid Lilith)

-Very territorial of Weiss and constantly declares she's Weiss fiancé multiple times especially around other potential harem candidates like Cecil and Karuta and only accepted Lilith as a second girl to Weiss.

-MC's hard work inspires her to become even stronger and is already much stronger than the point of the game where the story currently is.

-Power and personality has been drifting from the game and she starts acting a bit more like a villainess like giving people the "Looking at garbage" look to s*umbags and those who insult Weiss, although she's still pretty kind to her friends.

Allan

-Hero in the game and in the story

-Has nearly every stereotype of Main Characters from being able to grow faster than others in training, Cheat Ability and being a lucky pe*vert for some examples.

-His cheat ability (present both in the game and the story) has him be able to copy any spell he sees. (Later on he's copied plenty of Weiss custom and personal spells which annoys him)

-MC's efforts greatly inspire him to double his efforts and become stronger and is able to keep up with the MC and corner him, although has yet to beat him in a fight and such is the second strongest in their grade.

-Has a righteous persona which gets him into conflict and rivalry with Weiss, although later on their relationship improves, but Weiss still keeps up his tsundere persona with him

-Cynthia was suppose to become his lover after his childhood friend Shari dies during a school outdoor activity.

Lilith

-Weiss Maid with skills of an Assassin

-Initially scared of Weiss but warms up to him after MC wakes in Weiss body

-Joins MC in school

-Has threesomes with Weiss and Cynthia

Shari

-The Hero Allan's and Duke's childhood friend.

-Was suppose to have died in a school outdoor activity but is saved by the MC (Who remembered how sad her death was in the game and remembered how it caused some players to quit)

-Initially hated Weiss for his attitude and poor reputation but warms up to him and they develop a friendly/brother-sister relationship with him after finding out his real personality.

-Has a crush on Allan

-Acts as the straight man of their gang.

Duke

-The Hero Allan's and Shari's childhood friend

-Was a main charcter in the game along with Allan and Cynthia

-Acted as the "Bro" character in the game and in the story, but in the story he has a friendly relationship with Weiss as well and acts as a "Bro" character him him too, despite Weiss constantly hurling insults at him calling him "Protein" for example.

Karuta

-A minor character in the game who was suppose to have been kicked out of the school early on and never seen again but was saved by Weiss in the game,

-Saved by the MC in exchange for her to teach him flight magic

-In love with the MC and is a harem candidate

Orin

-Trap Beast Tamer who looks like a cute girl

-Able to sexually confuse Weiss, Allan and Duke due to his cuteness and to the annoyance of Cynthia and Shari?

Cecil

-A strategist and gamemaster who gave advice to the MC during the final fight against the Demon Lord

-Falls in love with MC after he spends an entire day playing board games with her

-Most brazen aggressive of the harem candidates and openly challenges Cynthia and claiming if their engagement is annulled she would go straight for Weiss