It's a purely narrative game, the original version (this is now a remake of a remake in a new engine) was made in RPG Maker but without any RPG elements. Walk around, talk to NPCs, watch the story unfold.

The one big thing it has in common with Undertale is that the less you know going in, the better. If the art style and vibe is enough to get your attention, go ahead and give it a shot, go in blind.