Rukia Kuchiki started out as a
Shinigami (Death God), but in the
first episode she gives her powers
to Ichigo Kurosaki. She met Ichigo
and when they were fighting a
Hollow, and when she got hurt she
told him to stab her sword into him...
and he did, which changed him into a
soul reaper! She then enters a faux
body and convinces Ichigo to help
her in her work as a Shinigami until
her powers return.
After a while, her older brother
comes and takes her back to Soul
Society. Giving away her powers was
a serious crime punishable by
execution. Ichigo and a few others
then go to Soul Society to rescue
her.
Rukia Kuchiki, when sent from the
soul society to vanquish a hollow,
she runs into Ichigo who causes her
to get injured by the hollow and
consequently ends up giving him all
of her powers rather than half. She
then helps him do her job as a soul
reaper until the soul reapers Renji
Abarai and Byakuya Kuchiki come
and take her back to the soul society
for committing a capital offense
(giving her power to a human) as
they try to kill Ichigo.
Rukia has lived ten of Ichigo's lives
(you do the math) and that she
inhabits a Gigai (fake body given to
disimpower soul reapers. Also she
likes anything to do with rabbits and
draws very poorly. Personality wise,
she's kinda weird.