Thanks for the suggestions, yes I mean real time 3D games not VNs, because it's different there in terms of gameplay.
As I said above such things will be optional (turned on from the settings since the game does not focus on that and a lot of people will want to ignore it), but I like your idea about spawning a little companion for a short period of time + the visuals of bigger stomach for a duration.
The companion will have to be spawned by pressing a key similar to the parasite by the way, I don't want to add a full-time follower for reasons related to scope of the project.
By the way, you can open a support thread with a 'feedback' tag on Discord with all of your ideas there.