A lot I haven't seen or read, but the ones I have do not trigger my Gary Stu alarm bells:Here’s the character I like.
- Takumi Usui from Maid-Sama!
- Yuuji Kazami from The Fruit of Grisaia
- Anos Voldigoad from The Misfit of Demon King Academy
- Sasuke Uchiha from Naruto
- Kazuma Yagami from Kaze no Stigma
- Hajime Nagumo from Arifureta
Imagine if one of these characters is the protagonist of some Japanese isekai harem story, it would be quite enjoyable~
Sasuke is arrogant and so consumed by his vengeance that he almost ruins everything for everyone multiple times throughout the series.
Hajime is also extremely arrogant and uncaring towards basically everyone, and a huge part of the story is him (re)growing as a human. Not that he gets all that much nicer towards people outside his family.
Your last sentence is funny, given that at least Arifurety is a Japanes isekai harem story, though one that breaks from a few of the prominent tropes with a main character that is aware that the girls like him as opposed to being as dense as a neutron star, and a canon harem ending (decided before the last chapter even) as opposed to the open end we often get.