Spam offering tail service until there's an event where you meet Grimwald the first time, then he will appear randomly in the tavern, and grind Bond points, after there's enough then go offer tail service and it'll trigger his Bond Story
Where is the tavern
I didn't see him in the tavern, I saw him once offering services but never saw him again after that.
Try set the recommended dish to be potato, it attracts rock-type Pokémon iirc
