Tarmiel is one of the four archangels. Despite the three heads, he only has one personality. He was a decent minor protagonist. But my least favorite archangel.
Tarmiel and Sariel work together all the time. We get to see them fight the Ten Commandments during the original holy war. Unfortunately, due mainly to their arrogance, they go from dominating the battle to begging for help. After seeing Mael die, they give up their bodies to seal away the demon race.
After most of the Ten Commandments are defeated after being broke free, Tarmiel, Sariel, and Ludociel find bodies as vessels to end the new holy war.
Tarmiel and Sariel end up fighting Estarossa of the Ten Commandments to get revenge as he was the one who killed Mael.
His grace is Ocean which allows him to attack his enemies with waves of water. Pretty impressive but he doesn’t really defeat anybody with it
When Estarossa becomes too strong, they give up their vessels and emerge with their original bodies.
They find out that Estarossa really is a corrupted Mael cursed by the original Gowther. Unfortunately their fellow archangel was corrupted by The Commandments in his body even after Gowther’s curse was broken. Mael goes berserk and kills both of them. Rather sad way for them to die.