Present - Rena is of coures the new born daughter of Heero and Relena. (da) Though she's only appeared in the present time for a total of maybe two or three episodes so far you can't really make much of a profile on her. As they did with Haruka and Milliardo, Heero and Relena constantly fight over Rena's future role in the family. In this case instead of going against the whole training idea Relena encourages it while Heero fights against it. Being the only girl in the family Rena does tend to get more attention from Heero now that her big brothers, Haruka and Milliardo, are going to leave for collage soon.

Future - In a far off future where war is in every day life, Rena Yuy is among the few rebels that will go against a dictatorship run by Kuro Hidama. Rena along with her now only brother, Haruka, are the only ones left in their family and are among the last remaining of the Neo Gundam Pilots. This verison of Rena doesn't trust anyone as far as she can spit. One of the only friends she's been able to make since childhood was of course the daughter of the late Shingo Winner, Trina. After Nova found a way to get to the past to follow Hidama though time Rena became the first candidate along with Trina to find her and exterminate her if possible. Eventually we get into the main NGW story line in Part 2 where both girls fall on top of two familiar boys, Haruka and Shingo.