The coolest Master in another world.

I lived in a world without magic, no matter how hard I tried, I wouldn't be like the characters I read. I was bored until I was sent to another world with strange powers. From then on, I could become the most powerful being in another world.

He was trained by a Yandere who happens to love the god who reincarnated him, and she put him through rigorous exercises to make sure he didn't keep needing the god and get in the way of her romance.

The protagonist is a Chuunibyou who only cares about being the coolest no matter the situation.
https://zetrotranslation.com/novel/being-the-coolest-in-another-world/