 If you liked
Arifureta Shokugyou de Sekai Saikyou
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 ...then you might like
Sekai Saikou no Ansatsusha, Isekai Kizoku ni Tensei suru
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Both shows are isekais, where our main character is betrayed and turns into an OP white hair dude, both are merciless due to their own nature and both uses guns, also both find a group of girls that with those will carry out their misdeeds, esthetically the shows also look similar, from the title, the OP and tha animation (but in the last one I think that is better done in the Aristocrat anime)