Isuki's village was scoured by samurai collecting taxes needing provisions making the villagers suffer. When the village was raided for the umpteen time the goddess Ukanome speaks with Isuki and grants her a magical weapon. With the divine weapon she sets out on a journey against the "bad samurais".
Itsuki and her fellow peasants a light version of Tohoku dialect, mixed with "country bumpkin" style speech style. Itsuki is a twelve year old and speaks with a U.S. Southern accent. Itsuki has some "magical girl" traits (her taunt and joke weapon especially).
She doesn't appear directly in Sengoku Basara 3 or Sengoku Basara 3 Utage. However in Sengoku Basara 3 Utage, she sent a contribution.
And in Sengoku Basara 3, Date armies and including Masamune make reference about the promise to her and the peasants.