Sakuya's Final Familiar Form is a double-edge sword ability in Rewrite that lets Sakuya turn into a giant familiar; capable of destroying the world.
In this form, Sakuya has the appearance of giant Dragon-like creature with purple wood-like skin, with a muscular build (Indicated by its six-packs), horns on each side of its head, large demon-like wings; noticibly there seems to be energy resembling fire surging from the lines and joints on its body. The familiar possibly has no legs as its lower body is like a dome in which a 'Cherry Blossem Tree' stands. Also, Sakuya's human can be seen strapped to the familiar's chest.
Chihaya's Route: Akane kidnaps Sakuya and infuses his body with the energy from many hot spots which causes his transformation. As the Dragon-Familiar, his colossal body begans to drain the Earth of its energy which would soon cause its destruction. When Kotarou attempts to reach Sakuya's human form on its chest the Dragon's chest, the Dragon blocks his path with its giant branches but they are burned away by Kotarou's new ability. Kotarou assults Sakuya's human body which makes him wake up and dispels his familiar form.
Moon Route: As Sakura Kashima's poison filled familiars fill the sky above the Moon Kagari, Sakuya transforms in order to protect Kagari; only this time he has full control of himself in this form. Sakuya's branches catch the familiars in the air while getting poisoned as a result, eventually his form withers and crumbles; reverting back into a 'Cherry Blossem Tree'. Even so, the tree continues to protect Kagari but it too withers from the poison and dies; Sakuya disappears from all realities as a result. (Or does he?)
- Life Draining: Because of its colossel size, a single contract from Chihaya can not support it so it has the ability to suck life directly from the planet.
- Branches: Sakuya's branches can be used to attack or hault his enemy's advances; as stated by Kotarou, the branches felt like the toughest things that he's ever tried to cut, even though he was using Idea Overdrive which strengthens his aurora.
- Endurance: The familiar has a thick outer shell and extreme vitality which is likely strengthened through Sakuya's will. Even when its Dragon form crumbled from the poison in the familiars, its Tree form continued to destroy the familiars.
- In the Moon Route, Sakuya possibly used Rewrite to transform into the dragon.
- Sakuya's death in the Moon Route is known to be one of the saddest moments in Rewrite.