Mariko (マリコ, Mariko)
Mariko is usually seen as cold and emotionless, because she is no longer human. She's a reanimated Corpse.
However, she happens to have a little more attitude and feeling then we are original exposed to; first shown when she voluntarily thanked Kaito for saving her and again, when she asked the Doctor (Soga) to go with Kaito instead of following her master's (Soga's) orders.
Kaito is also the first (but not only) person to treat her like a human girl and protect her from harm.
It is suggested that Mariko still has a human side which is growing with her feelings for Kaito, this, even the Doctor didn't realise could happen.
Power (パワー, Pawā) Results in superhuman strength due to Mariko's reanimation. She can lift things physically impossible for the average human, yet is not phased by it. She also feels no pain, making her very difficult to deal with in a fight. She has displayed the strength to lift hulking altered with no stress to her body in any way whatsoever.
Soga: The Doctor is her Master. Soga found her and took her in as a nurse after she was reanimated by a certain unknown alter. It's later revealed that Soga is her Father and that he is the one who reanimated her.
Kaito: Despite her claims that she does not feel emotions, Mariko is shown to be blushing at Kaito at one point, implying a romantic interest/sibling bond with him. They have feelings for each other, most likely originating from when Kaito first treated her like a girl. Mariko has protected him a few times, and vice versa.