Ultra Cannon is a blast of concentrated cursed energy fired from the small gun installed in hand of respective cursed corpse.
Kokichi used this technique first time in conjecture with his Ultimate Mechamaru against Panda who is able withstand. the destructive properties of the attack.
When used in Mode: Absolute, its destructive properties are increased drastically and it consumes one year worth of cursed energy that Kokichi had saved up.
- Jujutsu Kaisen Manga: Chapter 38 (p. 8).