Lexaeus
Lexaeus, the Silent Hero, is number V in Organization XIII and one of its founding members. He appeared in Kingdom Hearts: Chain of Memories during Riku's storyline, working with Zexion and Vexen to try and manipulate Riku into serving them. Lexaeus wields a large tomahawk in battle, using his enormous strength and the power of Earth to combat his opponents.
In Castle Oblivion
Organization XIII first appears in the series during the events of Kingdom Hearts: Chain of Memories in Sora's storyline. Much of the Organization members' activities centers around the rivalry and strife within the Organization itself. Lexaeus is heavily involved in this feud, which originates from spite between senior members of the Organization and younger members like Marluxia and Larxene.
When Larxene and Marluxia begin to show signs of dissent, Zexion and Lexaeus begin monitoring the castle and their activities. Also active in the castle are Axel and Vexen, two other members of the Organization. Axel is too unpredictable to trust, but Lexaeus and Zexion enlist Vexen's help in spying on Marluxia. After learning that Marluxia plans to make use of Sora's power by deceiving him into feeling loyalty to Naminé, they decide to make similar use of Riku.
Confronting Riku
Vexen tries to make use of Riku's power by gathering data on him and creating a replica, but his experiments are interrupted. Though he succeeds in creating the replica, he is killed by Axel on Marluxia's orders before he can achieve total control over it, and the replica becomes independent, searching for a heart.
With Vexen gone and the replica useless, Lexaeus takes matters into his own hands, and the Nobody appears to Riku shortly before Sora confronts Axel and Marluxia at the top floor of Castle Oblivion. He tries to sway the former puppet of Xehanort to give in to the darkness inside him and use his full dark powers. Riku refuses to cooperate, and Lexaeus attacks him, hoping to destroy him if he can not be manipulated. Despite his incredible strength, Lexaeus is defeated, and with his last breaths, releases all the darkness within him, enveloping Riku. He is nearly overcome, but in the end King Mickey comes to Riku's aid, and his light overcomes Lexaeus' darkness.
Lexaeus in Battle
Lexaeus is exceptionally strong physically, and uses the element of earth to reinforce his attacks. He regularly strikes at Riku using his enormous tomahawk, and can hurl it into the air only to have it come down and flail about the combat area. Like several other Organization members, Lexaeus has the ability to levitate, which is the only magical abilities he displays. He does have some other supernatural abilities, however; Lexaeus can dig out chunks of rock form the floor and heave them at Riku, and can also strike the floor with such force that it tilts.
Links
Video of cutscenes before and after battle with Lexaeus
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