JoJo no Kimyou na Bouken: Adventure

Both anime have main character that fights agains some sort of evil. Both main characters have som sort of alter ege, but while in Baoh Raihousha the main character changes into it, in JoJo's Bizarre Adventure main character summons it. Both are old school OVA with lot of violence, even gore. Both anime feature parasites that resists in human brain. 

If you liked or did not like the OVA, you should check out the newer adaptation by David Production. Sure the colors aren't as accurate to the manga like the Ova is in some parts, but the story is told much more faithfully to the original manga. Also the dub is better than the OVA's dub. 

Well although Jojo's Bizarre Adventure (2000) is the "new" season it's also the beginning of the series ... anyways this two anime's have almost the same idea, except Jojo is more violent and bloody than Shaman King. But in both anime's the main character has the ability to summon a spirit which helps him through his journey. On there journey they make friends that have the same ability and they join him on his mission to fight against evil!