It's also entirely possible that it's not actually Koume, and she let "that girl" use the costume. She's nice to ghosts like that.
Morikubo's going to take a break...Wait- a dead end!?We've got you cornered now, Sachiko-!Now, nowWait, you guys!As... as expected, I just stand out too much not to be noticed!I can't go any further~~Fufun~!Um...What's this~Hmm...Get back here, you-!It's only natural! Of course I found the perfect hiding spot!Why haven't you picked up on my aura of cuteness?!Return to the first panelYou don't stand a chance of catching the cute and clever Me!She came out all on her own...Shhh-Fufu...Where could Sachiko have gone~There's no trace of Sachiko anywhere~If she's not here, thenThe game of tag can continue-!