Hope form is an original drive form I made
So as you know, most drive forms need a certain party member to activate
I always imagined if Sage was an actually Kingdom Hearts character the game would have a 2 player mode where you pick which twin you play as
The form would only be accessible in 1 player mode and I think it'd be called Hope form as it would use whichever twin you're not playing as and your clothes would look like theirs (Soras clothes would take on the blue, pink, and green of Sages clothes, Sages cloths would take on the black and reds of Soras clothes)
I still need to decide what Hope form would do but I'm thinking since you take on the power of the other twin, it'd add their stats onto your own (adding their attack, magic, and maybe even their hp) and I'd have it be a dual wielding form with your second keyblade being whichever one the other had as their main (in this case Sages second keyblade would be the Kingdom Key, while Soras second would be Sages keyblade Natures voice)