Ryota (MC) dies in real world, and drops from a slime in the Lv1 of a dungeon in isekai (yup). He meets a girl who lives in the dungeon because she can't afford rent, and discovers three things:

1. everything in that new world is produced through mob drops
2. his max level is Lv1, so he won't level up, ever
3. his drop skills are all S so he gets a lot of good stuff out of any monster that he kills

Run-off-the-mill isekai, but still fun stuff to watch in a rainy day.