When you get called by Akashi to the arsenal saying that Hiei had an accident and when you arrive, you see slightly worried Hiei... and this kiddo asking if you are "shikikan-chama"
Like, for example, an older looking Nagato. ...well, probably not a good example. Current Nagato is already pretty OP, so upgrading her further by turning her into adult is rather too much. Maybe... not quite loli, just flat, but how about a more older Queen Elizabeth, since current QE is kinda underwhelming as a battleship aside from her skill that boosts a HMS fleet.
Gameplay wise, it probably needs to be something quite different from a retrofit, much like how Belchan's skillset is different from Belfast. A bit of cynical thought, but I reckon that older versions of some ships would help pad out content. And also I think I'm thinking too much about the game regarding this.