Loke is a slim young man of average height, distinguished by his delicate facial features and his orange hair. While in his human form, his hair is kept in a mildly short, spiky cut, with spiky strands covering his forehead, and other, longer ones jutting upwards from the top of his head. As a Celestial Spirit, his hair is much longer, and kept in more numerous, larger spikes jutting in every direction, with a pair framing Loke’s face; due to another pair of strands, sitting on top of his head, being vaguely reminiscent of animal ears, the rest of his hair mirrors a lion’s mane. It's also worth noting that, as a Spirit, his teeth are sporadically portrayed as being sharp, in reference to his lion theme. Loke’s black eyes are almost always covered by a pair of azure-tinted sunglasses with a thin frame, with one of the only instances in which he was shown without them being during his time as Karen Lilica’s Celestial Spirit. While in his human form, his left ear is adorned by three earrings: initially, he bore a stud and two rings; later on, he was instead shown donning two studs and a flower-shaped earring. His Fairy Tail stamp is located on his back. Among young girls, Loke is widely reputed as a greatly handsome man, being top ranked as the “Mage you want to have as a boyfriend”

While initially introduced as a member of Fairy Tail, Loke wore a green coat with a wide collar, complete with prominent, spiky, brownish white fur trimming lining the hood, over a light red shirt covered in many flower-like motifs, black pants and whitish sneakers, each adorned by a pair of light green stripes. Later on, his attire received some changes: his coat was given a more prominent collar, darker in color and sporting some lines vertically going up it, and his shirt was replaced by a darker one bearing on the front a menacing skull, with its eyes being hidden by a pair of bands crossing his face; in addition, he switched his black pants to a lighter, looser pair, complete with many pockets reminiscent of small bags, and, similarly, donned lighter shoes, each bearing three bands around and before the ankles area.

As a Celestial Spirit, Loke’s outfit (that he can change using a type of Magic) is radically different, consisting of an elegant dark suit, with the jacket left unbuttoned and the loose pants held up by a light colored belt, over a lighter shirt, with a zebra-striped tie (portrayed as plain red in the anime) around the neck, plus dark shoes. When he appeared to defend Lucy Heartfilia from Bickslow, his fingers were also adorned by two more rings other than the one he uses to cast his Magic: one of them had an "X" shape, the other was plain, and both had edges in relief.

As Gray Fullbuster’s partner during the S-Class Trial, due to the heat of Tenrou Island, he donned a green T-shirt bearing the writing “Manage” on the chest area, mildly loose, light plus fours, and light sandals.

Loke (Leo the Lion) was contracted to the Celestial Spirit Mage Karen Lilica. Karen was an abusive master to Aries, often mistreating or directly hurting her. One time, she even used her as a shield against attacks. Just as she was about to sentence Aries to seven days' imprisonment in the Human World, which is thought to be fatal to Celestial Spirits, Leo appeared in her place. Due to her wicked and abusive nature, Loke demanded that the pacts with him and Aries be removed and that he would stay in the humans' world until she did so, easily resisting Karen's attempts of forced closure of his gate.

By staying in the human world, Loke prevented Karen from summoning any other spirits for combat, thus taking away her ability to perform jobs. Karen made several attempts to persuade, beg, trick, and coerce Leo into returning to the Spirit World, all of which he refused, much to Karen's anger.

After three months, Leo became able to endure the pain of being in the Human World. Believing that Karen had been punished enough, he decided he could forgive her and if Karen abused Aries again, he would defend his friend. However, he learned soon that Karen, in desperation, had attempted to complete a job without her spirits and had been killed by another Celestial Spirit mage. For violating his contract with Karen and causing her death, he was forbidden to return to the Celestial Spirit World. Soon after, Leo disguised himself as a human named Loke, and joined the Fairy Tail Guild as a Mage.

Macao arc
Loke is first introduced with some women. When Natsu ends up brewing up a fight, he comments that it's noisy, and tells his women he'd join the fight, which makes Lucy say he corrupted his image. When Gray Fullbuster asks to borrow Lucy's underwear, Loke comments that they have no grace and takes Lucy to a different area. He is about to use his Magic to end the fight like everyone else, but he is stopped by the guild master Makarov. Makarov also reads off charges against Loke for flirting with Council Member Elder Rage's granddaughter; a talent agency charged them for damages as well.

Lullaby arc
He is seen at the beginning with Gray, and also flirts with Lucy yet again. However, he realizes that she is a Celestial Spirit Mage and runs away, Mirajane stating that he must have had a bad experience with one in the past. He runs back to the guild to inform Natsu Dragneel and Gray that Erza is back. Mirajane also says that Loke had tried flirting with Erza and had nearly got himself killed. He's seen standing away from Erza, sheepishly murmuring that he might go home.

Loke arc
The gang first meets Loke upon completing a mission in Balsam Town. They wander over to find out that Loke had a mission in the area (before running away from Lucy). When Lucy goes outside with Plue and Happy because the others were engaged in a serious pillow fight, she is assaulted by bandits; however, she is saved by Loke. Loke then states that his job was to capture them. As thanks for saving her and to chat, they go to a local bar together, with Loke still being afraid of her. Lucy, thinking that their conversation is completed, gets up to leave, but Loke stops her and then hugs her, announcing that he will die soon. Realizing that he didn't want to get her involved, he then states that he was joking and that it was just one of his pick-up lines.

This makes Lucy so upset that she slaps him and storms off. The next day, Loke's girlfriends are at the guild, upset that he had broken up with them and are looking for him, confronting Lucy when Mirajane calls out to Lucy for help, which results in them thinking that Lucy is the reason Loke left them. Lucy is suspicious of what he said the night before, and summons Crux to do a search on him, finding out about Loke's history and former owner Karen Lilica. Gray then bursts into Lucy's room, saying that Loke had quit the guild and disappeared. Lucy decides to go look as well, thinking she might know where he is.

Lucy goes to the area Loke is at (Karen's grave). She reveals she knows Loke is the Celestial Spirit, Leo the Lion. Lucy asks why Loke is still in the human world. Loke says he's stuck and has been for three years, but is now losing his ability to stay in Earthland much longer. Loke reveals he cannot go back because he killed his master, Karen Lilica. After telling Lucy his past, Loke finally starts to lose his grip and tells Lucy goodbye and asks her to tell Fairy Tail that he's sorry. She tries to save him by opening his gate so he can live back in the spirit world. Loke begs her to stop and says that he deserves to die, as it is the rules. Lucy, however, shouts that she would change the rules and tries to forcefully put Loke back by using her spirit energy. Noticing this, the Celestial Spirit King appears himself.

He explains that although Loke did not directly kill Karen, it was still his actions that caused her death. In an attempt to convince the Spirit King, Lucy summons all of her current Gold and Silver Keys, stating that saving your friends is not a sin. It amazes Loke that she could summon this much at once, since it requires a huge amount of energy, although they quickly disappear. The Celestial Spirit King, seeing Lucy's resolve to save her friend, allows Loke to return to the spirit world since he realizes Loke only disobeyed Karen for the sake of Aries. Loke says farewell, and as thanks for saving him, gives her his key.

Loke reappears at the guild's makeshift bar, surprising Natsu, Happy and Gray with the revelation that he is a Celestial Spirit who looks human, much like Virgo. When asked what spirit he is, Lucy reveals that Loke is Leo the Lion, much to Happy's delight to the point that he drooled on his shoulder. Getting a bit too flirtatious with Lucy, she nearly closes his gate, but he stops, saying that he has something to give them first: tickets to a resort hotel.

Fighting Festival arc
Before Lucy is finished off by Bickslow's strongest attack, Baryon Formation, Loke rushes in without being called and saves her before she's hit by the attack. Loke appears to have a totally different look, with his hair extended into a lion's mane and a black suit; Loke states he has come to fulfill his promise with Lucy.

Bickslow mentions that he always had a feeling Loke was a Celestial Spirit; Loke responds that hurting his owner is something he can never forgive. Bickslow laughs and reminds Loke that he's never once beaten him in a fight. Loke orders Lucy to stay back, however, Lucy refuses and states that Celestial Spirits aren't shields and that she would fight together with Loke. Happy whispers that "they're a cute couple", making Lucy shout at him.
Eventually, Lucy entangles Bickslow with her whip and Loke finishes him off with his Regulus Impact attack, knocking Bickslow out in one hit; he then makes a light saying "I Love Lucy" for Lucy to which Happy whispers "He llllikes you". After Lucy falls down, feeling the affects of summoning two Ecliptic Zodiac keys, Loke returns her keys and says that he will always be there when she needs him. He later makes a brief appearance at the guild with Lucy as everyone celebrates and recovers.