Isekai de Nekomimi Seijo to Tsundere Elf

The protagonist tries to save a girl from a random attacker but ends up losing his life. Afterward, a god-like being reincarnates him to save another world.

Reborn as Haruki, he meets Philia, a cat-eared saint, at a church, and the two set off on an adventure together. Haruki’s… ahem essence becomes a source of magical power, and the closer he gets to Philia, the stronger her magic grows, leading to rapid development of her skill.

However, Philia must undergo a ritual to become the Great Saint, and Haruki has to part ways with her temporarily. While fighting solo on the battlefield, Haruki one day encounters an elf…

[Translated from dlsite]