Sorry for an upcoming long message but i just kinda wanted to leave all potential suggestions at once, maybe some of them will inspire you :)
- Lactation: pretty self explanitory, it would be fun to have a mechanic where the salvor could "drain" herself once her breasts start getting too big for example, or maybe it could even work as a sort of distraction, leaving a trail of milk someone to lure away potential threat for a while, or maybe it could be an effect from some suspicious foods, causing her to have a constant lactation state Or she could just milk herself for the fun of it if she starts getting used to it 馃槄
- Idle events/Chat: i think it would add alot to the game if we could just have a little chat with salvo outside of story progression or scripted events, while she is idle, like a dedicated "start a conversation" button call it simply "chat" maybe she could share her feelings, thoughts and such with it, which could maybe also trigger some special interactions, say she feels silly now and tells us to use the echo graph cause she saw something only for us to see her flashing a boob in her hand or spanking her butt or something like that, maybe when she is anxious or uneasy we could compliment her to boost her morale, or while she is really stressed she could relax herself and ask if its ok to masturbate in order to let some of the stress out. Since a good portion of the game is text based it would be awesome to just have various optional events and chats with her when nothing in particular is happening to her, it would build her character by a lot and give her more personality and also interactibility for us, since we have a Y/N we could either be nice and supportive or mean and indifferent with our responses making the "protect her or not" aspect of the game even more complex. i also simply think it's entertaining to have a silly moments with a protagonist in a horror esque enviroment, she does look like a type of person to do silly and lewd things for the fun of it, i really liked the marco polo exchange and wish for more interactions like these 馃槄
Cumflation: since the deep depths are knows for its big creatures, maybe once they engage with salvor, they would be so overwhelming for her, that they would fill her up, causing her to slow down significantly for a limited time until she drains all of it out one way or another.
inventory menu: assuming salvo can only hold so much stuff maybe we could have a little pop up menu, where she could choose what to get rid of / leave on the ground Bonus points if that menu had a little preview of salvo and how she currently looks from front and back (to enjoy both of her sides at any time) kinda like in an rpg game On that note (although i'm not sure how feasible that would be) it would be nice to see a little customization for salvo, maybe have a single different hairstyle or swimsuit to choose from Or just tell her to go naked from the very beggining of the mission that could also be a nice option before every mission
On a technical side of things, i think the chat log text could be a little bigger in my opinion
Aaaand that's it, i hope you may find some of these interesting or helpful :)