[alvinkhorfire]

^
Your answer is in the following summary, tsunade666. Full credit for Elf song for the answer.

Originally Posted by Elf song

Finished vol.21

Spoiler for Short summary of XXI:

Yuji took Kazumi with him to Seireiden to use her "image" of the City to reverse the Tuning Spell with "Anti Seal"(from vol VI (Dantalion's arc in the anime but animators changed the story) which will cause the already unstable dimension around Misaki City to break down, thus opening the Interval between worlds; where he would created the Xanadu.

Yes, I know that the translation of full Novel Volume 22 text in Baka-Tsuki is almost complete. Still, I would appreciate if anyone could post a summary of that volume, like the ones posted in this thread a long time ago. A summary would definitely help people like me to understand the finer details of Volume 22. Thanks to anyone who can provide such summary.