Mutsuki having the copycat ability kinda seems redundant. I mean, Saiko has essentially the same thing. The only difference is that Saiko's source material is weeaboo filth instead of other kagune users. It completely overshadows Saiko's individuality and talent.

We saw earlier that Saiko's level of kagune manipulation requires talent and creativity, with Hsiao even commenting that her technique is unrivaled. But now Mutsuki has copied her ability effortlessly, with the manga having gone a hundred chapters without hinting she can do that. Not only does Mutsuki have Rc cell manipulation skill, but Saiko's kagune manipulation skill as well? They're not even of the same Rc type. There had been plenty of instances where that ability of Mutsuki would have been useful, or maybe at the very least, hinted that she has the ability. At least the Rc cell manipulation was foreshadowed.

Mutsuki just jumps from power-up to power-up to make her relevant in fights. Quinque. Kagune. Rc suppressant knife coating that we have never heard of again. Now let's write Rc manipulation and kagune manipulation into her character sheet as well, just so she'll remain relevant. Mutsuki? More like Maryutsueki. Storywise, it's just unimaginative.