* New types of enemies. Maybe instead of fiends we can have Youkai like Kitsune, Tengu and Nekotama.
* Rachel, Ayane and Momiji as playable characters.
* Kasumi and Hayate could be playable as either unlockable or DLC.
* Rachel's gameplay I think could use some refinement. In place of the hammer and gun, I'd use give her an axe, whip and sword. She'd be faster than her previous incarnations but not as fast as the ninjas and with a Pankration influenced fighting style. More spells that play up the rose and snake themes would be nice to and maybe integrate her moves from DOA 5 Ultimate. Her close range abilities would in theory be the most powerful of the cast.
* Momiji is the Glass Cannon and is better at long range combat. In team battles she'd handle crowd control well. More flame based attacks.
* Ayane is the jack of all stats.
* Kasumi is the lightning bruiser hitting hard and fast but not as versatile.
* Hayate uses a stance system of two styles: Mugen Tenshin and Karate. Mugen Tenshin focuses on sword skills, teleports and ninpo wind skills. Karate is a bit closer to beat em up.
* Tag team combos between characters like DOA would be nice. I.E Rachel and Momiji have a move in which Rachel ensnares opponents in her vines which Momiji uses as a media for flames.