Huh. I wonder where this is supposed to go in the Mamange pool. I'll see if I can figure it out once it's translated. Edit: Found it. It goes right at the end of Chapter 14, just before Mamanga Eternal kicks off.
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You've become quite the big sister figure, haven't you, Hime.
Hm-hm-hm! ♥︎ A big girl, huh?
Eh heh heh...
Aaaah, no fair! Ei's gonna be a big sister too!
No need to fuss. You'll be able to become a big girl soon enough.