Lyght

Lyght is a party member in Act One of I Am Still Alive. He is the brother of Ray and a close friend of Gaines. He joins the party in Veril, when Emily and Osilus volunteer to accompany him to the Veril Spire (where he hopes to find Egon, or at least find out what happened to him) to ensure he comes back safely.

Lyght is killed off-screen when the Veril Spire collapses.

Emily
Lyght is distrustful of Emily and Osilus at first, but after the trio bands together, he decides to keep an open mind. Despite this, he seems to struggle with mood swings, getting angry at the other two at varying intervals. Emily and Osilus tolerate this, treating Lyght with kindness regardless.

Defeating Egon, however, drives him over the edge. He becomes enraged at the other two, blaming them for getting his hopes up. Emily is hurt by this, but mostly sympathetic towards Lyght, as she asks Osilus to find him and take care of him (seeing as she was the only way out of the Veril Spire.)

Osilus
When it comes to party members, Osilus seems to have a clear bias towards Emily, believing her to be capable of saving the world, as opposed to Lyght, who is doubtful. This leads to a miniscule amount of tension between the two.

After defeating Egon, when Lyght lashes out at the rest of the party, Osilus defends Emily, stating that despite pitying Lyght and understanding where he's coming from, he believes it isn't an excuse to lash out at Emily and himself.

Despite this, Osilus regrets his actions after Lyght leaves the party, and is willing to search for him while Emily continues onwards (due to him not having a way out of the Spire.) After the collapse, he asks the Old Hero if Lyght survived, and is surprised to learn that the Hero knew who he was talking about. The Hero then states that Osilus was likely the only survivor, and that he hadn't seen anyone else, which clearly saddens Osilus.

Ray
Lyght is shown to care more for Ray than any other character, citing to Emily that his only reason for keeping his emotions concealed is to avoid seeming vulnerable, to allow him to better protect his brother. Lyght leaves Ray in charge of the Veril group of survivors upon departing to the Spire.

Gaines
Gaines and Lyght seem to have a solid relationship, with the former doing his best to help Lyght handle his mood swings. Gaines does not put much stock in Lyght's position as commander, instead viewing him as a friend.

Old Hero
Though they have yet to interact in-game, the Old Hero has met Lyght in the past, as revealed after the credits in his statement to Osilus.