Bloodstained: Ritual of the Night

Quests are given by the NPCs in Arvantville - one lady requests items, another requests you slay demons and the old lady by the shop requests food. Fulfil 30 for the achievement.
I found that slaying demons is the easiest to complete and make the bulk of the 30. After the completing the first request, you can accept every other quest she has right at the beginning of the game - you'll probably slay all the demons she wants killed just playing through the game naturally. The other NPCs require you to complete each of their quests in turn and require lots of grinding for alchemy ingredients.