Mariko is watching the battlefield carefully, poised to intervene while keeping an eye out for anyone attacking her. She's tucked away slightly out of sight, watching Senju Tetsuma and the strange Uchiha fight. Her older brother had said that Tetsuma's one of their up-and-coming assets and assigned Mariko to protect him. The Uchiha is a wild card - Mariko hasn't heard about her yet - and appears strong; she's definitely keeping up with the Senju boy and has already managed to draw blood.
She's just about to activate a seal when something explodes behind her, sending her flying towards the fight. Both the Uchiha and Tetsuma are knocked off their feet, and the three kids go rolling together. Mariko curses as she accidentally activates the seal - all her seals, there must have been chakra in that explosion - and something comes swirling towards them.
The sky whites out, something roars, and suddenly Mariko's falling, tumbling away from both the others into nothingness.