Lea is the human form of Axel. In Kingdom Hearts Birth by Sleep, he appears as a teenager and a close friend of Isa. He appears as an adult in Kingdom Hearts 3D: Dream Drop Distance, in which he chooses to become a Keyblade wielder.
Kingdom Hearts Birth by Sleep
By the time Terra and Aqua leave Radiant Garden, Lea has conspired with his best friend, Isa, to break into Ansem the Wise's castle. When walking past the town square, Lea notices Ventus drop his Wooden Keyblade and picks it up, offering to give it back to him. Though Isa tells him they need to hurry, Lea tells him to lighten up since "it will only take a sec". He calls Ventus a kid for "playing" with a wooden "toy" and proudly takes out his frisbees, saying they are real weapons. Lea introduces himself and Isa and asks for Ventus's name. Once the introductions are done, Lea asks Ventus to fight with him, much to his confusion. Ventus agrees with a smile while Isa looks on with an amused chuckle.
Ventus beats Lea handily, leaving him winded. Lea tries to wave it off by calling the fight a draw, only to be teased by Isa. The three of them laugh, and Isa reminds Lea that they have to go. Lea then tells Ventus that they will meet again someday, because they are now friends. Isa asks Lea why he keeps "picking up stray puppies", and Lea tells him that he wants to live forever in the memories of everyone he meets. The two look up at the castle, and Lea asks Isa if he is "ready" before they leave together.
Sometime after Terra-Xehanort is defeated and taken in by Ansem, Dilan throws a struggling Lea and a resigned Isa out of the castle as Aeleus looks on. Afterward, the pair go to the Castle Town to buy sea-salt ice cream from Scrooge McDuck, and they look up to the sky as they eat.
Between Kingdom Hearts Birth by Sleep and Kingdom Hearts 3D: Dream Drop Distance
At some point, Lea and Isa's hearts were consumed by darkness and transformed into Heartless; this event happened in Ansem the Wise's computer room, along with the apprentices. However, their strong hearts and wills allowed their bodies and souls to continue on as Nobodies. Organization XIII recruited the pair, naming them "Axel" and "Saïx" and inducting them in as Numbers VIII and VII respectively. However, the two joined the Organization with a plan to take it over.
At some point during Sora's journey, he destroys Lea's Heartless.
Kingdom Hearts 3D: Dream Drop Distance
Some time after Axel sacrifices himself to give Sora safe passage to The World That Never Was, Lea has a dream of Roxas reminding Axel of the promise he made to him and Xion, to always be there to bring them back, and he awakens in Radiant Garden, with his memories of his time as Axel intact. Discovering that four of the founding members of Organization XIII, Aeleus, Even, Dilan and Ienzo, have been recompleted as well, Lea notices that Braig and Isa are missing and decides to look for them. After talking with Aeleus in Ansem the Wise's study, he finds out there is no one else in the Castle. Deciding to check the castle grounds, Lea is told by Aeleus not to bother. Ienzo explains to Lea if Braig and Isa were recompleted, they would have appeared in the same place as the others. This makes Lea wonder if Braig and Isa could have been "blasted off to some other world", which Ienzo explains is possible if the world they came from no longer exists when they are reborn; they'd reappear in Traverse Town or a similar place if that was the case. Lea then finds the remnants of Ansem's notes about the Door to Darkness, and leaves to bring back Braig and Isa, without telling Ienzo and Aeleus how, complaining that he always gets stuck with the icky jobs.
Lea uses a Corridor of Darkness to travel to Disney Castle. From inside the Corridor, he disrupts the hostage situation taking place in the library, blocking Maleficent's attack against Mickey, Donald, and Goofy and distracting Pete long enough for Queen Minnie to escape his clutches. Once Maleficent and Pete are gone, Lea reveals and introduces himself to Mickey and his friends. Lea travels to the Mysterious Tower with Mickey, Donald, and Goofy, and he requests that Yen Sid make him a Keyblade wielder, shocking everyone present. After Lea is brought up to speed regarding Sora and Riku's Mark of Mastery exam and Xehanort's inevitable return, Yen Sid warns him that the road he has chosen will not be easy, but Lea decides to "jump right in" anyway. He is then helped with his training by Merlin, along with Flora, Fauna, and Merryweather, by using their magic to compress the time his training would take.
Learning of the danger everyone else is in, Lea arrives in The World That Never Was, just in time to save Sora from becoming Master Xehanort's final vessel in the new Organization XIII. His appearance shocks Xemnas and Xigbar, the latter of whom calls him "Axel". Lea explains that he'll always be there to bring back his friends, then jokes to Master Xehanort that he had plotted his "script" so well, but forgot to "write the sequel". Lea is attacked by a hooded member wielding the Lunatic. After deflecting the attack, the member's hood blows back to reveal Saïx, leaving Lea shocked to see his former friend as one of Master Xehanort's vessels. Regrouping with Mickey and Riku, Lea gives up on correcting people about his name and says they should escape while they have the chance. After Donald and Goofy arrive and defeat Xehanort's guardian, the new Organization begins disappearing, its members returning to their proper place in time. As they leave, Lea shares a final look with Saïx.
Back in the Mysterious Tower, Riku decides to go back into Sora's dream to awaken him. Lea tells Riku if the darkness gets him again, then he will be there to get him out, joking that "Dark Rescue" is his middle name. After Riku succeeds in awakening Sora, Lea then joins him and the others in a tea party while Riku is recovering. Once Riku wakes up and Yen Sid declares him a Keyblade Master, Lea tells Riku that he'll catch up to him in no time and become a Keyblade Master as well. Despite Sora and Riku's disbelief, he explains that he came to the Mysterious Tower to learn how to wield a Keyblade and even planned to be using one when he showed up to save Sora and Riku, but hasn't been able to summon it yet. Wondering if the problem is in the way he moves his wrist, Lea tries one more time and successfully summons his Keyblade, shocking everyone present.
Afterwards, Lea soon returns to Radiant Garden.
During his youth in Radiant Garden, Lea 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.
After being revived following Axel's demise, Lea wears the black coat he wore during his time as Axel and appears identical to his former Nobody, only lacking the tear-shaped markings below his eyes, and having a slightly darker skin tone.
Lea is both childish and competitive, willing to disrupt Isa's schedule for his impromptu 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 realized they couldn't escape and barely moved. He is also somewhat smug and sarcastic just as Axel was.
He wishes for everyone he ever meets to remember him, so he can live on forever through people's memories. Like his Nobody, he uses the phrase "Got it memorized?" on multiple occasions.
As an adult, retaining his memories as Axel, Lea becomes as cocky as his Nobody counterpart, to the point that he actually challenges Master Xehanort while defending Sora, even though he would be using his chakrams against Master Xehanort's Keyblade. Even so, he retains his competitive streak, demonstrated when he states that he intends to compete with Riku in the art of the Keyblade.
As a teenager, Lea is not physically shown fighting, though he has an offscreen spar with Ventus and loses. His weapons during that time consist of two red frisbees with black edges, each adorned with a Bomb design, which later influence his choice of weapons in the Organization: chakrams.
Upon reaching adulthood following his Nobody and Heartless's destruction, Lea wields the fire-controlling chakrams once used by Axel, and after Sora and Riku's Mark of Mastery exam comes to an end, he reveals his ability to wield a Keyblade that bears features from his chakrams, the Bond of Flame and Frolic Flame Keyblades, having received a magically compressed training session from Yen Sid, Merlin and the three fairies.