No one knows. Or rather it was never actually explained outside of "Merry's power has gotten stronger".
And no Renko can't do the same thing.
Oh, ok... it would have been nice for Renko to do the same thing too...
We're friends, aren't we?Right, that'll be ¥1000!♪The important thing is you had fun.Siiiiigh. That was awesome!♪.... Whoa! So this is the world on the other side!?Okay, okay. Then this should do it...Shake
ShakeMerryyYYyy, I wanna see the world on the other side, tooo!