Kasumi

The Eternal Heroine
Once a Ninja of the Mugen Tenshin Ninja Clan, she escaped and became a nukenin ("missing shinobi") after learning her uncle Raidou had raped her mother decades ago and that Ayane (who was enraged at this too) wasn't just her best friend but also her half-sister, and he came to her village to steal the Torn Sky Blast Ninja Spell, crippling Hayate, Kasumi's brother in the process. She learned that Raido was taking part in the Dead or Alive Tournament, and went on to win the tournament and defeat him, however, unknown to her, the DOATEC corporation that created the tournament had experimented on him and used the tournament to test his strength, and afterwards Raidou revived as a monster. With the help of Hayabusa Ryu, she defeated her now monstrous uncle once and for all. However, she was captured by DOATEC for use in her experiments, and eventually helped to escape by Ryu again. On her way out, she meets Kasumi α, a clone of her who thinks they are "sisters", and fights her after discovering she knows her brother is in the facility. She finds her brother after escaping who seems to have amnesia and coerces her into fighting, after beating her, she faints, and Hayate recovers his memory and goes on with Ryu to fight Kasumi α and a brainwashed Ayane set up by Genra, a now traitor member of the clan. She goes in hiding afterwards to escape her former clan's assassins seeking her, and pretends to be a normal high-schooler. She finds his brother, who alongside Ryu and Ayane are triying to track down Genra, and "fights" her as it is code to kill traitors, but "loses" and she escapes. She finds later that the Mugen Tenshin are planning an attack on the DOATEC HQ after their transgressions against their kin, and decides to infiltrate the HQ herself to stop DOATEC from attacking her family. As she finds with the DOATEC CEO Helena Douglas, a midified Kasumi α renamed α-152 was their ultimate weapon, and was about to be activated, so helena tries to kull Kazumu but is stopped by Ryu who made his way through the building while helping the Mugen Tenshin. Afterwards Kasumi confronts, but α-152 was too strong and escapes in the chaos. Kasumi disappears again after the intents to assassinate her become stronger, meanwhile another clone of Kasumi was made with her memories and escaped the facility.

Season 3
Now this clone seeks to find α-152, and the lack of a Dead or Alive Tournament happening has left it to the conclusion that the most likely location must be the TFR ring.