Season 1

In the war against the nightmarish creatures known as Horrors, Mankind's most formidable line of defense has always been the power of the Makai Knights. But now, one by one, the Knights are being mystically marked for death by a mysterious magic user in a crimson mask. Even Kouga, the bearer of the golden GARO wolf armor, is among the afflicted, with the accursed mark slowly draining his strength, and making the use of his armor incredibly painful. Who is the Red Mask and how has he (or she) been able to target the Knights so effectively? All signs point to a betrayal from within their own ranks and now it's up to Kouga, Rei, and the other Knights to track down their enemy while they're still strong enough to defeat him!

黄金に輝く狼の鎧を纏う魔戒騎士・ガロとなり、魔獣ホラーをはじめ数々の巨悪に勝利してきた男・冴島鋼牙は、その功績により番犬所を束ねる“元老院”付きの騎士として、名実ともに最強の魔戒騎士として名を轟かせることとなった。 ある日、いつものようにホラーを退治した鋼牙は、赤い仮面を着けた謎の男により“破滅の刻印”を刻まれてしまう。自分の命を蝕む刻印の痛みに耐えながら、鋼牙はガロとして宿命付けられた新たなる戦いに身を投じていく。