He is the main antagonist in Yo-kai Watch Shadowside: Return of the Oni King.
- Yo-kai Watch Shadowside: Return of the Oni King: Antagonist
- Yo-kai Watch: Wibble Wobble: Playable Yo-kai
- Yo-kai Watch Shadowside: Minor Yo-kai
Onion Rasen is a silver overweight Oni with grey armor.
In his De-Armored form, he loses a few pounds. His speed has also significantly increased.
In his Fragment form, he resembles a four-armed shadowy figure.
Yo-kai Watch Shadowside: Return of the Oni King
Oniou Rasen is known as the most dangerous threat to the Yo-kai World of all time. The Onimaro Leader uses Touma to bring Oniou Rasen back. He is first seen crashing down from the Onimaro meteor and lands in a neighbouring forest. After Touma is cured by Natsume and Kitaro, he emerges from the forest, cutting down a skyscraper with his sword and building himself a throne, before absorbing every Onimaro on Earth, including the Onimaro Leader, with the exception of Ogu, Togu and Mogu. Oniou Rasen is killed by Fudou Myouou and Yami Enma.
Yo-kai Watch: Wibble Wobble
His name translates into Oni King Rasen (Japanese: 鬼王・羅仙 Oniō Rasen).
- When he gets beheaded by Touma, he manages to stab Touma with a fragment of his blood, which is a reference to Shuten doji from Japanese mythology.
- A fragment of his which appeared in SS022 went by the name of Kabila.
- He is the second Boss Yo-kai after McKracken to share the same name on both forms (both their names of their second form are unchanged).