Additional farming spots not mentioned here can be found in Mifune's 2★ form page.
Warriors aid each other. I swear to fight until this body is ash and dust, to bring about your wishes.
I fully understand your wishes! In order to improve myself, now and forever, my life is yours.
I have touched the demon blade's true power. Its soul and mine are now intertwined, and will continue to fight so long as I live.
There are few remaining records of his life even after he was resurrected by the demon blade's power in the war with the gods in Grand Gaia, though he was said to have fought ferociously. It is unclear what heights he could have risen to had he continued his training after that point. He might have fully absorbed the demon blade's power into himself, becoming one with the weapon and slaying gods with an absolute power beyond human understanding.
Trivia, Additional Information & Notes
Mifune's 1 hit combo attack is similar to Iai, a one hit, sword-drawing attack technique from Japan, in which the wielder draws the sword from its sheath, strike the opponent, and immediately put it back in the sheath. This attack will mostly cause the enemy to be severely injured, or even instant death.
Mifune is the first unit to skip the 7★ evolution and instantly evolve to Omni evolution.