(This is for the fanfiction "Crossover Together". Info may change from canon information)
Lugia, in his human form, takes on the appearance of a young adult. His hair is silver and smoothed out similar to Yugure Kagayaki, and his eyes blue like Nagisa Shiota. His outfit is similar to that of a prince: a silver overcoat lined in a blue line going over a snow white under shirt. His overcoat flared in the back in two 'tails', lined with blue as well. He wore silver pants reaching to just above his feet as well.
In his true form, he holds a more draconic-like appearance: he has silver skin, and blue fins along his back, and wings resembling hands. His mouth is a beak ridged to resemble sharp teeth.
He was one of the leading Angels of Elysium alongside Celestia, but when one of his Future Sights predicted his involvement and full power in the end of the world thanks to Sombra, he felt that running away was the only option, and left the Overworld completely. His legacy lived on for many years after this, many angels unsure if he even existed after a long while.
While he didn't appear officially, he has been shown in his true form in his island, sensing that Nagisa Shiota got his Halo Blade.
On the night prior to the group leaving to London, Lugia went into the dreams of both Nagisa Shiota and Yugure Kagayaki, and gave them both a set of Future Visions to better prepare them for the upcoming future.
He officially appears within Synapse, confronting Nagisa Shiota within the dream realm and properly introducing himself and giving his praise. He admitted that he would've contacted them all if it wasn't as dangerous as talking to just one of them. He then told Nagisa a bit about future Sight, and that he believed there was no way to avoid them, before showing him the aftermath of Pluton's attack. When asked how it'll happen, he admitted that he didn't know, but was sure it'll happen. He then stated Aladdin was grateful to have him as a friend just before the dream ended.
Sometime after, He then contacted Yugure, and gave his thanks on their efforts, but only to find out that Nagisa Shiota had gone missing. He was able to give Yugure a future sight before her dream ended.
Not long after, he found Nagisa's soul within Synapse, saying how worried he was for him. When asked if he died or not, Lugia questioned on what weapon he used, and then said he will be revived since he used the Miracle Sword, but he also added in that he will be teleported away to an unknown located, stating that magic wasn't consistent. He offered to give him another future sight, but was declined.
While not officially appearing, Lugia was contacted multiple times by Nagisa, and he only left him with visions: Gakuho Asano shooting Heine Wittgenstein, Karma Akabane getting killed by Karasu, and Envy's capture by other Homunculus.
Lugia was rediscovered by Nagisa once again, Lugia fully convinced that Heine and Karma were now dead. He however was found by the rest of Team Harmony (much to his and Nagisa's surprise), and finally shown that they can and will change the future if they have to. He claimed that they were the very first to do so, but refused to reveal where he truly was.
Aladdin and Hoopa end up on his island, and they soon found his true location within the island's caverns. Despite being pleaded with to return, Lugia ultimately refused, and didn't reveal to them why, and that it shouldn't worry them. When the others arrived, he was about to leave the island when Sombra finally confronted him. He was ready to accept his fate, but was saved by Morgiana, who drove him away. Despite the save, Lugia fled the island.
Heine Wittgenstein followed him, and after a long while, finally managed to convince him to return to Elysium, mainly to show that he was alive to his fellow Angels. After being told the situation, he told them that as much as he wanted to, he can't help them with this danger and that even legends have their limits. He finally admitted to his worry in his future sight, and his fear that Sombra would use him to destroy the world. With him now known however, he feared that Sombra would not rest until he has him. He met with Nagisa after the meeting, and was presented a "backup plan" in case he does control him. He gave Nagisa Shiota one more future sight, calling him a true hero.
Throughout the final fight, he was isolated with Ciel Phantomhive within the 3-E Building, though he thought it was just prolonging the inevitable, which came true when Somnbra did find him. He failed to escape, and was soon controlled by him, forcing him into his true form and unleashing his true power on Tokyo. He was only saved after Nagisa sucked all of his power alongside Sombra, and released it to the Surface World. He appeared two weeks later in the hospital to see Nagisa, and explained to him that his act had connected all three worlds together, and that they all are now apart of eachother.
Lugia has the very rare ability of Future Sight, alongside Sombra. He believed that these visions couldn't be altered until after seeing Heine and Karma alive, the future altered for the first time.
Not mentioned by name, he is shown to use a highly powerful magical beam, and is presumably his strongest weapon used in his true form.
He is able to turn from his "true form" into a "Human form" at will.