Nevermind, decided to incorperate both aspects of the idea
Name: Yukiko Tsugumi
Age: 19(Note: I know twins have to be the exact same sage, but I forgot what age I made suzuku. For now, just pretend that the two are the same sage)
Sex: Female
Rider Designation: G4/Another Agito
Personality: Yukiko is the exact opposite of Suzuku, while Suzuku is kind, caring, and compassionate, Yukiko is cold, brutal and a loner. She is more confident in herself.
Bio: During the siege of Suzuku's home, Yukiko and Suzuku were separated from one another, Yukiko fled with one of her Uncles: a man who wanted to take over as King. Days ago, he made a pact with the OverLord: The OverLord offered him the world, if he helped set him free. The OverLord betrayed him, burning the city and the kingdom to ruin. He fled the destruction, only to be swept away to another world, into Agito world where the OverLord's destruction would continue. Sense then he had been training Yukiko, with the help of people from this world into a weapon of war, a tool to use against the Unknowns.
Like most women in the Tsugumi family, Yukiko exhibits strange, and unusual powers: she is a psycho-kinetic, and her future-seeing powers are far stronger then that of Suzuku's. For years, he taught Yukiko how to fully utilize her powers, turning her into a cold, merciless killer. One day, Yukiko overhears how He despised Yukiko's family, and how he was the one who unsealed the Over Lord, enraged by this Yukiko kills him without a second thought. This caused her to go berserk, destroying everything in her path
Realizing that Yukiko was too powerful to keep unchecked, they kept her in cryogenic hybernation, while the G4 armor was being constructed to keep her powers in check.
Years later, when nearly all of humanity is almost wiped out, they re-awaken her, to resume the fight against the Unknown.
Also, would it be alright if I gave G4 a weapon that's like the Funnels/Bits in Mobile Suit Gundam?
Also, forgot one other thing:
For the most part, when she speaks she'll talk like she's a machine. Only when she becomes Another Agito, she'll start to slowly regain her humanity. She'll be seen wearing a mask most of the time, or her face shadowed.