Throughout Celtic's lifetime, the relationships she's sprouted have been limited and not very plentiful. Almost all of her relationships with others have been unpleasant or violent.
Easily Celtic's favourite living being, Saxon has proven that there exists something that can match her in combat. Despite them fighting to kill one another, Celtic has found herself taking a liking to Saxon as a rival, and has done her part to ensure no one kills him before she can, just as he does for her.
"Hannah" and Celtic both respect each other as fellow Hive members, but that's as far as it really goes. They dare not consider each other friends, and hardly ever interact with one another unless they have to. The only times they do interact are when they're fighting over who gets what part of the animal corpse, or if they're coordinating on a mission.
Takeo Misaki and Celtic never once have had a violent interaction, strangely enough. It was Celtic who introduced him to the Hive with Hannah, and provided translations for what the Queen said to him, even if she did joke with the words a bit.
Celtic was responsible for the destruction of a large part of the Red Army, and loves to visit their traitorous Hive to cause some trouble whenever she can.