Miu Kawasaki

Ayumu Aizawa who can't recall his childhood. He doesn't suffer from amnesia but his younger days are a mystery to him. When asked to spend the summer with his father in Tana, a rural town two hours away from his home in Tokyo, Ayumu refuses as he has not seen his divorced father in four years. He gets bribed by his mother with a mountain bicycle and reluctantly agrees. Unbeknownst to him, this fateful trip will put together bits of his past. Soon after arriving at Tana, Ayumu encounters strange happenings such as meeting a mysterious boy called Wakkun, who lives in an enchanted forest, and floating orbs of lights appearing in the sky.

The characters receive an email from Ovan requesting them to go to Δ Hidden Forbidden Festival where a mysterious summer festival is set up. There they encounter an AIDA Chim Chim who wishes to peacefully co-exist with the players of The World. It then transforms into the word "Returner", which Haseo assumes it to mean that Ovan will return to The World.

The Digital World is becoming so overpopulated that the super computer Yggdrasill who governs the Digital World can no longer handle it. Its solution is Project Ark: to wipe out most of inhabitants with the X Program. Yggdrasill chooses a very small percentage to be moved to a new Digital World and then proceeds to destroy the old one. Some Digimon who were not chosen survive anyway, and they move to the new world with a rare gift known as the X Antibody; this antibody changes their appearance and makes them more powerful, while at the same time making them immune to the X Program. No longer in control, Yggdrasill uses the Royal Knights to destroy these X-Digimon, who are outcasts in the new Digital World.