Shin Walford

Shin Wolford is the main character of Kenja no Mago. After dying of an unknown cause, he reincarnated into an unknown world carrying with him a vague memory of his previous life in his previous world.
Shin tends to approach his new world of magic through a lens of his old world of science.

He later becomes the fiancé of Sicily.

(Source: Kenja no Mago Wiki)