Hello!
It is an option that will be added in later updates. I'm still considering what functions to give it specifically. For now, I think that when you advance enough in your relationship with the girl in question, select "Special" and a series of options will come up, including asking her to be your girlfriend, asking her out on a date, and up to 5 options that you already have. they will occur to me.
Currently, this option only has an in-game function and is part of Nana's Personal/Rival quest. Talk to her first and then you need to talk to Katsune and select this option to continue the quest. But this may change in the future.