(I saw a video of different hsr bosses ult's and got inspired)
I once made some posts of a yuu who overblots due to being the vessel of the villain chernabog from fantasia, they were manipulated and driven by him to the point of desperation allowing him to take over their body and cause destruction whenever he passes, inside the mind he continously tried to drive them to the point of insanity
Grim was the phantom of course
Another fairly recent idea was for them to become a jester, overblots when cosuming their victims tend to let their face visible, and some other caractheristics that can ve reconizable but mc's would be covered head to toe in a twisted jester costume
The blot twisted(heh) and riped their flesh appart, mutating and transforming their, their body is taller with almost pointy neddle like fingers their bones growing from the inside out and riping the skin out they look like a uncanny monster you'll se in a analog horror
A sight of pure gruesomnes, worst part of all?
They feel so much pain because of this, they're rotting from within the overblot half waiting to kill crowley and the other half waiting to end their own suffering
So in the first half of their battle when overblot yuu is on the floor coughing blood and ink from their lungs, a light shines from the sky eveloping their now ink covered deformed form, they slowly stand up hesitating and apprehensive
They feel the warmth of the light, of the star eveloping them into a faux embrace, the first comfort they had in what seems like forever time seems to flow so slow when you try to survive another day right?
They lift their arms to the sky like a follower asking for guidence from their god, and for once it seems like they will finally go home...
Only for them to fall onto the ground squirming in pain like insect who's just have been squashed, yuu's screams were loud inhumane and painful to hear, their voice impossibly distorted
A light so bright explodes from the body eveloping the room in seconds
Your body now stronger than ever, your rage as clear as white
So my take is, their "phantom" is a hrs boss version of a almagamation of all disney princess and heroes, but maybe like som like irom tomb or aquila all i think now its that it has a giant tail for legs, four arms and many details alluding to the disney heroines we all love, all lending their own fustrations to help one in need
(The reason why i put "phantom" in parentesis is cause the "phantom" is made out of energy rather than ink, so its head is a big fiery eye(like that of aquila)
Also this is all par of my theory/headcanon/oc of yuu being twisted of/is the evening star (or evangeline for some)