Open world game, but it's mainly a dating sim
In Skyrim and Fallout 4, I really liked the idea of having a romantic partner that is also your follower. You can explore the open world with your loving waifu tagging along beside you. Such as how you can romance Aela in Skyrim, or Curie in Fallout 4, and they can also accompany you as follower npcs as you visit various places.
My only problem is that open world games usually focus on combat and killing, but put the romantic stuff in as an afterthought. Like if you visit a beach, you're most likely gonna be there to 1) fight enemies or 2) go fishing. There won't be an option to, say, just take your waifu follower npc there to engage in some fun beach activities to build your relationship. No volleyball minigame, no building sandcastles with her, no surfing together, or other bonding moments like that.
You also wouldn't be able to take her to snowy mountain and simply have snowball fights with her or go snowboarding together. Romantic stuff like that is usually absent in these combat-driven open world games.
I mean, some visual novels are ok and all. But their gameplay is just clicking through menus and is honestly boring. It'll be cool to have a waifu follower in a 3D open world game. Being able hold her hands like Ico's Yorda and go sightseeing the world and activating fun minigames at various locations. Maybe with photography and taking pictures along the way. The games that really inspired me to write this post were 1) Skyrim and 2) Twilight Princess. There is a small fishing section in Twilight Princess where you can hang out with one of the game's more fleshed out characters, Hena. She can chat with you about various subjects in her cabin as you get to know her better. And she can also accompany you as you go out fishing together, instead of going fishing by your lonesome.
This is what I mean by fun activities. It'll be nice to play a 3D open world game with waifu followers npcs, but with dating sim aspects that are actually fleshed out and fun. There doesn't need to be any combat or killing whatsoever. It could be an Animal Crossing or Harvest Moon slice-of-life world where you just visit various locations with her and do fun things together.