Who is xion in Kingdom Hearts

That is not true she is infact a experiment that vexen made.she is a hybrid clone crossed between sora and kiari and isn't technically a nobody.
when sora is in castle oblivion in Kingdom Hearts RE: chain of memories her and roxas are there and both have no memories but when sora regains him memories roxas and xion get them to making xion go a bit loppy at the fact she isn't really her. she then goes searching for kiari thinking she is her other half but roxas and axel try to stop her from leaving. when she dies she dies in roxas's arms and fades into the light making him cry (emotion o.O?) and he then desides to leave orgy 13 o.o but axel then goes looking for him but see's him smiling (actually hhappy) with hayner, pence and ollete so he desides he wants his best friend to be happy and leaves him there.