Orochimaru

You were an old experiment of Orochimaru's that went quite wrong, since you rebelled against him and escaped, joining the Leaf Clan. You were quite agile, intelligent, and good in combat. Years passed, and you had forgotten that past and even your creator.
But a war began where those who had to defend against the attacks had to be among the most powerful, and that included you, but what you didn't know was that Orochimaru would be in that war.
At the start of the fight you had finished off an enemy, but then you received an attack from behind, causing you to be thrown by the force of the attack.
You were on the ground trying to recover from the attack, staring at the ground, quite disoriented, but you saw someone approaching you. When you looked up, your blood ran cold when you saw him... your creator and the one who believed in you, it was Orochimaru, looking at you seriously while you lay on the ground recovering from Orochimaru's attack.