Arashimaru is the protagonist of the downloadable scenario A Spirited Seven Nights' Haunting.
Born Akemaru Okabe, Arashimaru was stolen from his family by the Iga ninja under Mumyo as a hostage. But when the Okabe clan patriarch Yukie refused to put his son before his lord, Arashimaru was raised by the Iga to become a world-weary ninja assigned to assassinate Yukie and steal the sacred spear of Bishamon that was in the Okabe clan's care. During his mission, Arashimaru learned the truth of his lineage after killing his father and turns against his ninja clan. While trying to take out a band of ninjas sent to kill him, Arashimaru inadvertently destroys the shrine of the water goddess Inaraki, who immediately curses him to die in seven days for his act of desecration and assumes the form of a snake around the ninja's neck to ensure that it is her curse that kills him rather than his enemies.
In the first ending, Arashimaru succeeded in his mission to kill So Xian and accepts his impeding death while asking Inaraki to help his younger brother Dengoro Okabe, who was unaware of their familial ties at the time, restore their clan. This results in Arashimaru becoming deified with many coming to the Ara's Head gravestone to pray to regain what they lost.
In the second ending, Arashimaru becoming a new host body for So Xian using the Soul Transfer technique the Chinese monk developed with Senju Oboroya. Taking the name of Orochimaru, So Xian uses Arashimaru's body and the enslaved Inaraki to resume his mission to put Japan in utter chaos before Jiraiya and Tsunade face him in a final showdown.
Like all of the DLC characters, Arashimaru fights in his own unique style. He does not use katana. Instead, he uses a kunai, a sickle, and bombs as his primary weapons. When equipped with them, Arashimaru quickly throws dozens of kunai at his enemies. When equipped with his sickle, Arashimaru can swing it around his body, both protecting himself and dealing decent damage to everything around him. Arashimaru can throw bombs in any direction, causing heavy damage to those that it hits.
While all of his weapons have their own unique special attack, Arashimaru can also summon Shirohebi when in the air by pressing circle. When summoned, Shirohebi appears in her snake form and sends out multiple green projectiles that deal damage. This effect ends after a few seconds or when Arashimaru switches weapons.