Ichiro is first encountered in the Sunken Ship, in the chamber with the large pile of bones after Amaterasu floods the vessel with water by using Sunrise. Ichiro is created when the two demons Jiro and Saburo reunite in the water, with Jiro being the head of the creature while Saburo being the tail, and the resulting demon takes the appearance of a large shark with a vicious mouth of teeth and bears intricate armor plating on its fins, back, nose and tail.
Jiro and Saburo were originally a couple whose marriage was opposed by their parents. Having no other choices to stay together forever, they threw themselves into the ocean, committing suicide. Now, as the two demonic hermit crabs, they still long for each other, and Saburo will constantly attempt to dig through the ground of where they are encountered to flood the area with water, enabling her to reunite with Jiro. If this is to happen, then Ichiro will come as the result. And with its might, this abomination attacks fishermen and is widely considered to be one's end when encountered in the water.
"Jiro and Saburo combine to become the mighty Ichiro.
This shark patrols the ocean, attacking fishermen and causing trouble.
Meeting him in the water spells doom, but if you have a foothold on a boat or lily pad,
you can lure him close and attack his belly.
Doing so knocks him out and gives you a chance to attack."
When Ichiro emerges, it will be covered in armor plating, granting it invulnerability. Amaterasu has to destroy this armor in order to kill the demon, and she can do so by certain means: usage of heavy-damage techniques (especially Thunderstorm and Thunderbolt, since these armor are metal); repeated assault (Amaterasu can stay on a floating object (such as a lily pad) and attack Ichiro when it comes close. Rosaries is best for this) and usage of Rao's Prayer Slips (during the original encounter). When Ichiro's armor has been disengaged the demon will be stunned and can be damaged.
Ichiro is also susceptible to farming. After the armour is broken, Amaterasu can stand on a floating object and use Golden Fury and Brown Rage to farm it. Farming income is amplified by the Thief's Glove if it is equipped, and the hidden strike glitch can also be applied, though Ichiro has high resistance to damage. After farming procedures Amaterasu can assault Ichiro until its death and then use Thunderstorm or Thunderbolt as the Floral Finisher.
- If Jiro's armor was destroyed before Ichiro formed, it will start without armor.