Sakamoto was the leader of a cult called the Endwalkers and the main antagonist during the Endwalker Crisis. His cultists captured a few locals near End River and some soldiers of the Royal Army of Elysium. David and a few others from Elysium infiltrate them, then discovered that the Endwalkers were sacrificing people to the End. Which led to his ultimate capture and the destruction of his cult.
Before the events of Season 4, Sakamoto was a powerful, deranged practicer of End magic and using his gifts formed a End-obsessed cult and began preforming human sacrificial ceremonies to bring about the End. Which began the Endwalker Crisis between him and his followers and the monarchy of Elysium and it's army.
After knocking David out with some kind of spell, he ordered the Endwalkers to attack the army waiting above their secret hideout. The Endwalkers and Royal Army of Elysium did battle across End River. Using their End magic, the Endwalkers became invisible and teleported across the river behind the army. They then began battling the soldiers and Baron Randall Huntly.
Seeing the majority of his followers killed, Sakamoto tried to flee the scene but was cornered by a band of soldiers. He began to talk: "You would risk your life for your friends then you are fool for", before lageroun's apprentice, Guldir, knocked him out with a magical projective.
Life in PrisonEdit
He was imprisoned in the dungeons of Elysium. After a few weeks he became raving mad, preaching how End haa come and all are End. He is probably planning to escape and rebuild his cult, then take revenge on Elysium for his imprisonment and the destruction of the Endwalkers. This never took place due to the destruction of Elysium and the invasion.
The Blue Walk in the GardensEdit
David and C4ff were discussing about his gift to FMB - a giant golden spanner and their religion - in the Blue Gardens. Fearing their fanaticism, David tells C4ff about him planting a fake Holy Warhammer of Holiness causing some religious dissent, then wanted C4ff to plant more holy idols to weaken the Church of the Spanner. On the way David started thinking about releasing Sakamoto near Winterly Rock, but soon decided not to due to fear of him converting people into Endwalkers and preforming more human sacrifices.
It is unknown what happen to Sakamoto after the destruction of Elysium, but it is presumed that he was able to escape due to the lack of footage of his death. He could now be spreading and converting others to his cult. Before the invasion, he foretold the events that would take place in Elysium. He said that once Elysium was destroyed and the Porkborn dies, everything else ends, thus bringing the fate the Endwalkers once wished to happen.