Shadow Skill

Shadow Skill (影技 SHADOW SKILL, Shadō Sukiru) is a Japanese shōnen manga series written by Megumu Okada. An anime adaptation was produced by Studio Deen and aired on TV Tokyo in 1998 and has been released in the United States by ADV Films in 2005. An OVA series was released for 4 episodes.

Plot
Gau Ban is a boy who is struggling to become a "Sevalle," the strongest class of warrior in the mercenary kingdom of Guruda. Gau's elder sister, Elle Rag, is the 59th "Sevalle" and holds the honorable title of "Shadow Skill." Together the siblings fight magical monsters and historical warriors with martial arts, and the historical warriors chant the words "We are invincible!" and obtain superhuman powers.

Other Sources

 * (Manga)