Infinite Dendrogram: Volume 7 by Sakon Kaidou

Ray's arrival at Torne coincides with the beginning of the Windstar Festival, a joyous occasion that commemorates the defeat of an ancient evil.
But the mischievous hands of fate twist the celebration into a birthday. The once-slumbering entity has returned, and it is now ready to unleash chaos, suffering, and despair upon all in sight. Naturally, Ray Starling is not a man who can allow such a creature to exist.
The stars look down, the wind howls... but Ray soon finds his struggle intertwining with the life of a certain PK, and the matter of the missing Master.
Only one thing is certain in the carnage: They need a miracle.