Sturmig

Right. You should start the chapter Jabberwocky I from the beginning. If one of this tiles: "Wonderful Everyday" or "Hill of Sunflowers" is blocked. That means you have not got this ending yet. The order of obtaining any of this three endings is the same: Start Jabberwocky I > the right choice > Jabberwocky I ending >>> Start Jabberwocky II > WE/HoS > (End Sky II) ending.

Start Jabberwocky I and choose: "Who cares about that?" and complete the route. Then, start Jabberwocky II and you will get this ending. Keep in mind that you should get two other endings, before this choice appearing.