Lea

Lea is the complete being of Axel, and a close friend of Isa. He appears in Kingdom Hearts Birth by Sleep, as a teenager, alongside Isa.

Kingdom Hearts Birth by Sleep
While Ventus is in the Radiant Garden, Lea walks by, picking up the Wooden Keyblade from the ground. He asks Ventus if it's his. When Ventus responds that it is, Lea calls him a baby for 'playing' with it and takes out his frisbees. Ventus, not seeing them as much better of a weapon than his wooden Keyblade, calls them lame. The two introduce themselves, and then Lea calls for a one-on-one fight, finally prompting a smile.

After the battle, Lea calls Isa out for not trying to make up excuses for his loss and complains that he should've chosen Ventus for a best friend rather than Isa, causing Ventus and Isa to laugh. He then states that they'll meet again someday, because he and Ventus are now friends. After that, Lea and Isa walk off and look up at the castle, apparently 'ready.'

In the ending credits, Lea and Isa's plan is revealed, as both were seen being thrown out of the castle by Dilan with Aeleus looking on nearby. In the next scene, Lea buys Sea-Salt Ice Cream from Scrooge McDuck and gives one to Isa as they stare up into the sky.

Descent into Darkness
At an unknown point in time, Lea's heart was consumed by darkness, turning him into a Heartless. However, his strong heart will give him the ability to continue on as a Nobody: Axel. Some time later, Organization XIII found his Nobody, who received the name Axel and was inducted into their ranks as Number VIII. It is known that he joined alongside Isa, and the two had a secret, unknown plan.

Kingdom Hearts 358/2 Days
Lea does not make a physical appearance in the game, but Saïx calls Axel by his original name at one point near the story's climax.

Appearance
Lea appears in Kingdom Hearts Birth by Sleep. In it, he looks about the same age as Ventus. His hair resembles his Nobody's, but shorter and with the spikes styled upward. Lea has a slight widow's peak, a trait he also shares with Axel, though Lea's is more noticeable. Lea's eyes are also more of a blue/green color than Axel's striking green. He wears a sleeveless orange jacket with a white, sleeveless shirt underneath, and tan, baggy pants with red and white sneakers and black socks. The pockets of his jacket are a much darker shade of orange than the rest of it. He also wears a yellow and brown keffiyeh around his neck. The pattern of this keffiyeh changes abruptly near Lea's neck, from stripes to a very organized checkerboard pattern. Similar to Braig's scarf, the tip of Lea's keffiyeh is frayed slightly. He bears a curious resemblance to Hayner.

Lea carries around two red Frisbees with black edges, each adorned with a Bomb design, which later influence his choice of weapons in the Organization: chakrams. He lacks Axel's purple, upside-down teardrop facial marks in the actual game, but curiously they are present in his official artwork.

Personality
Lea is both childish and competitive, willing to disrupt Isa's schedule for his fight with Ventus. This is also evident during the ending credits when he is seen trying to escape from Dilan's grasp by flailing around his limbs, unlike Isa, who barely moved.

He wishes to be remembered and "Live on forever" so he attempts to make friends with people he comes across. Like his Nobody, he uses the phrase "Got it memorized?" on multiple occasions.

Trivia

 * In an issue of Famitsu PSP+PS3, Lea's name is misspelled "Lia". It was also once misspelled on the Kingdom Hearts Birth By Sleep official website, though it was later corrected.
 * Although it was a joke, Lea's statement that he should have been friends with Ventus rather than with Isa is blatant foreshadowing. In the future, his Nobody would choose to become friends with Roxas rather than stay friends with Saïx, Isa's Nobody.