This literally the third Isekai (that I know of) where the protagonist slime subordinate turns into a loli because it consumed a lot of power. Almost verbatim!
I get the feeling Miu might actually have feelings for him but is willing to let go for the sake of her moms and tak-kuns feelings. But then again, there's only so far she can support what she's doing.
And the only reason I see it going that way it's because it seems that would be the cliche...