Fuuma no Kojirou: Yasha-hen

Both anime are about rival ninja clans fighting each other in some epic battles full of violence, persecutions, traps and superpowers. 

Both '80s OVAs feature adolescents who are called on to solve ninja problems plaguing high schools. 

Both '80s OVAs feature ninjas with supernatural powers fighting their opponents to the death. 

Both anime are Jump adaptations from the 80's and are about a main character in a school fighting their way to the top. Both have a good sense of comedy, but also have great actions scenes which will keep you watching. 

Both stories were created by Masami Kurumada, and share some common features, specially bloody fights, exaggerated manliness and ultimate loyalty. In Fuuma no Kojiro you'll find several characters with almost identical appearance to the ones in Saint Seiya, since Kurumada uses the star system (popularized by Osamu Tezuka) in his works. Kojiro is Seiya counterpart (and vice versa). Ikki (Asuka Musashi) and Shun (Kirikaze) also have their doubles, and so on.