WARNING: The following contains spoilers for Season 1 of Shaman King (2021), now streaming on Netflix.
In the Shaman King reboot, Yoh Asakura finds himself torn between laziness and a life where he can relax, and a much higher calling as the Shaman Fight tournament rolls around. He realizes he could be a Chosen One like his grandfather, Yohmei, hoped he'd be, achieving godlike status so he can change the world for the better. But while Yoh initially comes off as a mystic who can simply channel ghosts and summon the dead, there are some caveats regarding how this works for his kind.
Early on, when Manta stumbles across Yoh in a cemetery, it's revealed Yoh's family descended from a line of seers who could communicate and harness ghosts. Yoh can allow his main ghost, the legendary swordsman known as Amidamaru, to possess him. Once he has a stick, even a wooden one, he himself can become this expert warrior. Here's how it works.
Interestingly, Yoh's shaman rival Ren confesses spirits aren't friends -- they're tools which should grant the user more control and allow them to harness more of the ghost. Yoh disproves this, however, because friendship means he can bond much more with Amidamaru and use more of their energy.
The extent to which this channeling can occur in Shaman King relies on Mana, which is basically the life essence of the shaman. The more Mana a warrior has, the stronger the bond with the ghost and the better they can become. Yoh also discovers the more belief he has in his Mana -- and the more positive and hopeful he is for himself and his ghost -- the stronger both will become in battle.
As Season 1 progresses, we also learn some souls can be trapped in bodies using tags. Ren's sister, Jun, does this to reanimate zombies, putting Pyron Lee's soul into his cadaver and making him a slave. It's something her Tao clan is accustomed to doing and has granted them power for centuries, even augmenting the corpses so the soul and warrior can affect more damage. Likewise, Faust is a necromancer who can raise the dead and form an army of trapped ghosts, so spirits can be put into play against their wills.
Yoh's fiancee, Anna, also has a unique take on necromancy as she can summon any soul from the afterlife and put them into Yoh. She did this for Pyron Lee's teacher so they could fight Jun's zombie. We also see Mosuke, Amidamaru's bestie, being put into Yoh's body, allowing the kid to use Mosuke's expertise and forge the Harusame sword when it got damaged. It's not just about fighting in Shaman King, but using the talents of other dead folks.
Last but not least, humans in Shaman King can transcend possessions or exorcism spells due to the Over Soul. This is where the bond's so powerful and the human has enough Mana, they can coexist with their spirit. The spirit can be wielded as a weapon, as seen with Yoh using Harusame, which contains Amidamaru's flame. In this case, the soul can act as both a sword and shield. Ren also bonds with Bason and uses the dead warrior as an extension of his spear.
Over Soul simply converts Mana to something corporeal. This is why we see Hao with his giant Fire Spirit, which is able to burn matter in the real world or cushion people when they fall from a plane. It's the ultimate goal as it allows warriors and their ghosts to really become forces to be reckoned with, but Yoh unlocks one final secret. Once the belief in his Mana trumps the other, his Over Soul stands a better chance of damaging that of his opponent.
