Almighty Supreme Beings
As the absolute ruler of Nazarick, Ainz has Mare's complete respect, admiration, and loyalty and he has pledged to serve him without hesitation. Originally, Mare believed that Ainz was a much scarier person, but is quite shocked when he and his sister witness his compassionate side that he shows to his subordinates. In the Siege of the Royal Capital, Mare recollects on when his master was teaching him how to destroy cities and leaving no survivors which makes him appreciate his master's kindness in helping him improve. He holds Ainz's words in the same realm as his creator and if any of the guardians told him the same thing he wouldn't be as moved or motivated.
Bukubukuchagama is Mare's creator. She programmed him to be a pushover who is constantly ordered around by Aura. This is because of her belief that the younger brothers should listen to their older sisters. She also dressed him like a girl, for some unknown reason.
Later during the Floor Guardians debate on having the young boys of the newly minted Sorcerer Kingdom wear girls clothes due to the misconception of Bukubukuchagama's tastes with dressing Mare up as a girl and Ainz's explanation of how she had specifically created this quirk for Mare alone and no one else. Greatly bringing much joy to Mare's heart and causing him to then emotionally express his happiness for his creator making something only for him and audibly expressing that he would allow no one but his sister to share the uniqueness that Bukubukuchagama gave him, showing that like his sister, Mare holds the highest respect, admiration and devotion towards his creator.
Mare is the submissive one of the two, with Aura always ordering him around. Despite this its been repeatedly shown that Mare truly cares for and loves his sister despite her usual dominance over him.
Mare appears to be quite scared of Albedo and stays clear of her whenever possible.
Unlike Aura, Mare is not programmed to argue with Shalltear. Because of his shy personality, he mostly stays out of their little arguments.
Mare gets along well with his fellow Floor Guardian, Demiurge. He often explains things to Mare if he doesn't understand him.
The two respect each other as fellow Floor Guardians.
Since Victim does not leave the Eighth Floor often, he does not meet him often. However, the two respect each other as fellow Floor Guardians.
Mare is close enough to Yuri to the point that they refer to each other with nicknames outside of work. This is because the Supreme Beings who created them were close to each other, and they felt similarly close to each other.
Out of all the other denizens within Nazarick, Titus would qualify as Mare's closest friend since they have a lot in common and prefer to remain alone and isolate themselves if they can. Aura has stated that Mare often visits the Grand Library and shares similar interests with Titus in literature.
Mare is a frequent visitor to the Grand Library, so the elder lich is accommodating to the Floor Guardian.
Mare is close enough to Pestonya to the point that they refer to each other with nicknames outside of work. That is because the Supreme Beings who created them were close to each other, and they felt similarly close to each other.
Mare is close enough to Eclair to the point that they refer to each other with nicknames outside of work. That is because the Supreme Beings who created them were close to each other, and they felt similarly close to each other.