Senna a care free girl with a secret. She is the collective of memories formed from the memory of the souls that were lost between the time and space that connect the world of the living and the Soul Society, among those souls was a soul reaper.
Senna first appears when Ichigo is surround by a new enemy known as blanks, She appears dressed as a soul reaper, After she deals with the blanks and kick Ichigo in the face she appears to have vanished, leaving a shocked Ichigo standing next to Rukia, all of a sudden a girl dressed in normal clothes appears dancing behind them, It is Senna in her human form, Ichigo and Rukia try to pry information for the over energised girl who seems more interested in havening then answering question. Frustrated by the girl Rukia returns to the soul society and tell Ichigo not to let her out of his sight. Before Ichigo gets to catch up with her again the tenth captain interrupts and tells Ichigo to come with him, where he is told of the Blank souls that were lost in the space between the worlds and have been stripped of their memories. The Valley of Screams is composed of these Blanks, but they alone could not be responsible for the size to which it has grown. He goes on to explain that the lost memories of the Blanks will have formed into a single being known as the Memory Rosary, Later Ichigo catches up with Senna Which results in a night of fun and laughter more for Senna then for Ichigo. Ichigo buys her a red ribbon for her hair, when she loses her yellow one that she never liked.
As the two being to grow close, Senna runs of and finds herself in a grave yard where her family is buried, All of a sudden she is attacked by a group of people wearing green armour and just is she is about to be taken away, Ichigo chops on the man’s arm who is holding her. With no where to stay Ichigo takes her home and the two stay up talking . The next day they bump into a small boy, who turns out to be a lost soul, As they travel looking for the souls father, Ichigo asks her why they do not send it back now and she replies, if this is his last memory then she wished for him to have fun ones before he goes. They find the sprits father who is also a sprit and the son leaves with his father to start their afterlife. Then all off a sudden, The Captains of the Soul Society confront Ichigo and Senna, explaining that she is not one of them but in fact is the Memory Rose and that she would come with them. Ichigo steps in front of her to protect her from them, Saying that she is here and now, she feels joy and happiness how could she be anything else then a person.
Before the argument can finish they are attacked by the strangers from the night before, this time they seem stronger and can use the blanks to grow back body parts, Ichigo tries to prevent them from taking Senna only to be knocked to the ground bleeding, Senna screams to Ichigo as he falls. Not giving up Ichigo finds a portal to the Valley Of Screams and tries to rescue Senna, but he is surrounded by Blanks and the group known as the Dark Ones (the pervious unknown attackers) Just as it seems impossible back arrives in the form of the Captain from the 11 squad and the battle turns, leaving Ichigo to faceGanryu the leader of the Dark Ones, as more of the Captains arrive and destroy the Dark Ones, time starts to run out for Ichigo with only one hour before the real world will be destroyed and then the Soul Society after the Valley Of Shadows enters our world.
Ichigo kills Ganryu, but it is to late and the world is about to meet its end, when Senna now controlling the Blanks brings an end to the process and in turn this means her death, Now lying dying after saving this world and the Soul Society’s She asks Ichigo to take her back to the graveyard her family is buried in, So she can see the name that is on her grave stone. Carrying her on his back he makes it to the graveyard and tell her that her name is on the grave, when it is actually blank. Unable to see in her weakened state she vanishes, Ichigo told her this so she would die happy believing that she once lived in his village, With the blanks gone so would the memory of Senna. But we see Senna again when a red ribbon that looks like the one Ichigo bought Senna early floats from the sky towards him and a girl runs past him who looks just like Senna.
Senna is later seen sat at another table in a restaurant during an episode.
Bleach: Memories of Nobody
The 1st Bleach movie.