Shirohebi, her actual name being Inaraki, is the main support character of the downloadable scenario A Spirited Seven Nights' Haunting.
When Arashimaru hid in her shrine, Inaraki took the destruction of her mirror by the ninja's explosive as an offense and places a curse on him where he dies within seven days. In order to ensure that he dies from her curse and not from his enemies, so she can save face with the regional gods, Inaraki assumes the form of a snake around Arashimaru's neck to protect the ninja in his mission to bring down his former ninja clan and its leader Mumyo. But as time passed, Inaraki developed feelings for Arashimaru and even consider renouncing her curse if the ninja apologized
In one ending, acting out Arashimaru's last request, Inaraki hangs with her comrade's spirit after he ended up being defied as one who finds missing things. In an alternate ending, Inaraki ends up becoming a slave to So Xian after he possesses Arashimaru's body and christens himself Orochimaru.
Arashimaru can summon Shirohebi during battle. When circle is pressed while in the air, Shirohebi will appear in her snake form and send out multiple green orbs that damages nearby enemies. This effect ends after a few seconds or when Arashimaru switches his weapon.