A Disturbance in the Forest Arc[]
Meeting with Rimuru[]
Having his entire tribe eradicated, Souei and his 5 remaining tribe members ran away with great regret, only to encounter a Goblin Rider patrol and later Rimuru. They fought due to the Ogre group's frustrations and a misunderstanding caused by Rimuru wearing the Anti-magic Mask, but it got resolved thanks to Benimaru's little sister's efforts and since no one died, Rimuru healed everyone with his potions and they all went into Rimuru's Goblin village, where a feast was about to be held.
After some rest, Rimuru learned about Souei and his companions' circumstances and asked them if they were willing to become his subordinates, even if it was temporary since they too would need to fight these orcs, it would be better to join forces. They asked for some time to think about it and walked away, only to meet his childhood friend and rival stating that it wasn't a bad idea after looking at the state of the goblin village Rimuru ruled over. After some frustrating reminiscence, finally decided to accept and finally, as a symbol of Rimuru's rulership, granted the six of them names: Benimaru, Shuna, Souei, Shion, Hakurou, and Kurobe. Thus, they all evolved from Ogres into Kijin.
Against the Orcs[]
Some days passed and Souei, Hakurou, and Benimaru trained together to get used to their newfound powers. Souei was particularly adept at using strings to decapitate his enemies and his using Sticky-Steel Thread to fight is Souei's signature move. Sometime after the Orc Lord's defeat, he becomes a loyal ally to Rimuru.
Attack of the Demon Lord Arc[]
He took part in the fight against Milim and Charybdis.
Visions of Coleus Arc[]
He helped Rimuru fight the Arch-Demon Gustav.
Human-Monster Interaction Arc[]
He took part in the battle against Falmuth.
A Demon Lord's Awakening Arc[]
After Rimuru became a Demon Lord, he evolved into an Oni.
The Octagram Soars Arc[]
He took part in the battle against Clayman's army.
Scarlet Bond Arc[]
He helped in the conflict against Lucua.
Conflict Between Saints and Monsters Arc[]
He took part in the battle against the Western Holy Church's forces.
Opening of the Monster City Arc[]
He takes part in Tempest's festival and is among the people watching the martial arts tournament. He was also tasked with observing Masayuki and later to investigate the western regions to find out who is causing Tempest's financial problems.