*SLIGHT SPOILER*
Axel killed Vexen because he was ordered to do so by Marluxia. Axel accepted Marluxia's order because he needed Marluxia's trust in order to do away with the traitors. Larxene and Marluxia were planning to overthrow the organization, and Axel needed a way to gain their trust and effectively trick them.
The only thing Axel's eliminated is vexen.
Vexen was killed frist by axel who was orderd by marluxia
Under Marluxia's order, Axel came to Twilight Town's replica world and stabbed and defeated Vexen after Vexen disobeyed proper orders. Axel wasn't on Marluxia's side, but he needed to gain Marluxia's trust to succesfully prevent Marluxia's eventual betrayal of the Organization.
Vexen was always kept under surveillance by the above-ground members of the Organization. There wasn't much trust between Vexen and Marluxia. Vexen eventually went against protocol by giving Sora the Twilight Town memory card, which was not ordered. He also informed Sora of Marluxia's plan, explaining to Sora who Namine was. Marluxia then ordered Axel to eliminate Vexen to prevent Sora from finding out the truth.
Vexen disobeyed Marluxia and personally crafted the Twilight Town memory card and a replica Twilight Town to reveal Marluxia's plan to Sora, because he always felt tension between the aboveground/underground members of Castle Oblivion. Consequently, Marluxia ordered Axel to eliminate Vexen when Marluxia found out.
Xemnas, Xigbar, Xaldin, Vexen Lexaeus, Zexion, Sai''x, Axel, Demyx, Luxord, Marluxia, Larxene, Roxas, Xion
xemnas, xigbar, xaldin, vexen, lexaeus, zexion, saix, axel, demyx, luxord, marluxia, larxene, and roxas. ... and then theres xion...
Sora first beats Vexen, but technically, Axel was the one who killed him, Sora then beats Larxene, and then Marluxia. Axel was thought to be killed, but he only faked his death.
Vexen is the nobody of Even
No, she is one of the puppets that Vexen created. For example, in Kingdom Hearts Chain Of Memories and Rechain of memories (the version for PlayStation2) he created a puppet Riku to lure Sora in so Namine could erase his memory so Vexen, Axel, Marluxia, and Larxene could have Kingdom Hearts for themselves. Yeah, they were going to use him. :0
Riku does not kill Axel... He is the only one to technically kill himself... He dies this in order to save sora from a huge mob of Nobodies. Axel even explains to sora as he says that's what happens when you put your whole being into an attack.
Xemnas, Saix, Xigbar, Xaldin, Marluxia, Larxene, Axel, Lexeaus, Zexion, Vexen, Luxord, Demyx, Roxas, and Xion, but she only appears in KH: 358/2