They made a mistake by just saying submarine. HG Wells wrote about a man exploring the ocean in a sphere. It was written in 1896. In the 1930s, the bathysphere was created. I don’t know if they were inspired by his story or if it was a coincidence, but it’s pretty cool either way!

There is a visual novel called Our Life: Beginnings & Always that may fit this. You can play as any gender, but I played as a female and I was very affectionate and doting to the boy in the game named Cove. You can choose to just be friends or create a relationship with him and it gives you a lot of control over how the relationship moves throughout your character’s life. He’s sensitive and shy, but as you get to know him he becomes very supportive and loving.

You play from childhood to adults and it’s very cute. I highly recommend it.