Based on no qualifications, but I've taken up drawing as a hobby:

-Bottom has eyelids

-Bottom has more attention given to the nose

-Bottom has lips and a hint of a chin

-Bottom has highlights and shadow in the hair

-Bottom has more proportionate eyebrows

These 5 things give an implication of a form. You probably also don't like the centralizing focus on Rem's iris. Rem is probably 5x easier to animate and 10x cheaper if she had to keep a form and be part of sequences up to industry standard https://www.youtube.com/watch?v=E_51cahT1NY (TW: Everything you hate about an*me). I just watched that video. The only shading Rem has is her neck, back of her hair, her maid frills, and under her bust. I have to imagine the woman on bottom either loses 90% of her detail when she fights (see the 1st Valley of the End in Naruto) or doesn't fight. She's more picture-esque. I spent roughly 2 minutes watching this one from Jojo's (another one with which I am unfamiliar) https://www.youtube.com/watch?v=bxwU6sSPpRk . It looks like the shadows don't move except between key frames, but they have relatively bountiful shading all around the face and body.

In short, watch Jojos and watch One Piece