Zelda – The Legend of Zelda
It’s surprising enough that Zelda hasn’t already gotten her own game. Yes, you could control her in Hyrule Warriors Age of Calamity, but even that was a spinoff, and Link was still the main character.
The “save the princess” trope is old, boring, and never leads to an interesting story or character development in Zelda’s case. Zelda as the main character, though? That would be fun and new and could also serve to help flesh out her relationship with characters like Link, Impa, and her father a lot more since she’s doesn’t just show up at the end of the game. Also, unlike Link Zelda actually speaks and can communicate with other characters verbally and have relationships with them.
A great concept would be for her to switch between her regular Zelda form and her Shiekah form from Ocarina of Time. Her Zelda form could use magic, whereas her Shiekah form could be good at physical feats and combat.
Zelda barely even feels like a video game side character at this point, I mean, the series is named after her. The Legend of Zelda is a masterclass in world-building and lore, but it’s not that great at relationship building or having interesting main characters. A game told from her perspective would help solve those issues considerably.