Infinite Dendrogram novel Volume 11 features story by Sakon Kaidou and art by Taiki.

An AI looks into the past, at an event long before Ray Starling set foot in the world of Infinite Dendrogram. The unstoppable Tri-Zenith Dragon emerges from the mountains. It is a bringer of death, wielding a miasma of desolation in its wake. The citizens of Altar can do nothing but watch as doom descends upon them. However... There are three who may be up to the challenge. Three Masters who, if they managed to work as one, could stop the imminent desolation of the land they call home. But with so much glory to gain, what could they stand to lose?