If I remember correctly (It's been a VERY long time since I've seen the anime, forgive me) the series starts with characters being possessed by a spirit that lets them fight with the skill of that spirit, but later the shamans channel the spirit into an object and let's them do cool spirit magic stuff, right? Which would you prefer going for? If it's the first, I think a Hexblade Warlock would fit quite nicely. They use Charisma for their attack stat, which would represent letting the spirit attack through them. You could even say that's your Warlock pact. You gain the spirit's strength in exchange for letting it use your body from time to time.
If it's the 2nd part, that's a little harder. I think maybe a Paladin would do well, since you can say your Smite attacks are you channelling the spirit's power through your weapon and such. Lay on Hands could also be channelling through the spirit too, as well as some of the spells. I think any of the Paladin Oaths would work well, so pick what you like