Wow... this is really... bringing chill to my bone. SO merry know about Yukari all along, and trying to stop Renko for going too far before Yukari take drastic measures? Why i have a feeling that this is how most of their adventures, they found something vital, yukari warn them and manipulate their memories, before giving them some complimentary gift.
From our point of view, Touhou is a game world, and Yukari is in it. Merry is on the other side and can see it, but its still in the game world, this a pocket world of a pocket world. The question is, which pocket is the larger one?
Merry's in the Touhou version of the "Real World" yet it is a small part of the Game world that is Touhou for us. Thus her reality is more the mirror of the larger reality that Yukari lives in. One day Merry will cross over, but Yukari wants her and Renko to wait until its time. Its possible something bad happened and Yukari's trying to make sure they have all the fun they can before IT happens. Or she doesn't want to lose those memories of her youth (before she was 17 years old, right?) and makes sure Merry gets to have them.
On the other hand, one day, maybe Renko does come over, but she and Yukari don't get along anymore and Yukari prefers to let them be friends as long as possible, before the lesser reality within the greater Game reality of Touhou closes on Renko and Merry forever.
I don’t know why, but... Renko said game world... however, how many continues does she have?... and the most importantly important question: If you DIE in the Game world, do you die in the real world?...
This is fine, though.
I'm having fun.
Entering the Game World, watching an eternal dream.
One day, I'm sure—
I haven't given up, though. I'll find some other way.
I'm telling you, it'll be great.
Hrrm... I really wanted to visit the Game World...