Isekai de Nekomimi Seijo to

The protagonist is killed while saving a girl who is being attacked on the street.  However, he finds himself reincarnated in another world, and is given the task of saving it.  He embarks on an adventurous journey with the cat-eared Saint Philia, whom he meets at a church.

During the day, they travel the countryside and fight monsters.

At night, the pair use their skills to raise their "ecchi-levels".