Reid Astrea/Relationships

Flugel
Not much is known about Flugel and Reid's relationship, however, we do know the two of them shared a similar relationship than that of Gian and Suneo from Deraemon series. From what the author had said, it's safe to assume Flugel was the "brains" and Reid was the "brawn" of the duo.

Flugel seemed to have respect for Reid's strength, enough to note him as strong, but also introduced him as a fool in the Pleiades Watchtower Trial.

Julius Juukulius
Julius and Reid shared a rather hostile relationship, despite Julius showing immense respect for the dead Sword Saint. The two battled multiple times. Initially, Julius proved vastly inferior to the Sword Saint, not managing to land even a single strike but after reaching his own resolve and reforming the contract with his Quasi-Spirits-turned-Spirits, the Spirit Knight managed to fight the Sword Saint on equal grounds and eventually even defeating him. Despite that, Reid remarked that if he still had his original body, Julius wouldn't stand a chance and the Knight wholeheartedly agreed on that assessment. In his final moments, The first Sword Saint showed a degree of respect towards Julius, asking for his name and congratulating him on passing the 2nd Trial of the Pleiades Watchtower.

Lye Batenkaitos
Lye and Reid shared an extremely hostile relationship. Reid usually didn't care about him and showered him with insults like "filthy midget-chan" while Lye tried to come up with an explanation as to why Reid was able to descend from his floor, before rethinking his strategy and ultimately deciding on eating him, which always ended with Lye getting beaten into a pulp and Louis taking over his body. Interestingly enough, not even Lye was able to establish a "normal" conversation with Reid.

Roy Alphard
Roy and Reid also shared a rather hostile relationship with Roy sole goal being to eat the first Sword Saint's name and memories which ended disastrously for the Sin Archbishop as Reid overpowered Roy's existence, taking over his body and achieving complete and utter revival, effectively coming back to life about 400 years after his death. Fortunately, Reid turned out to be incompatible with Roy's body, shattering and dying for the final time.

Natsuki Subaru
Reid and Subaru didn't interact much. However, he did kill the boy in several loops, as he found him to be "disgusting". However, due to the first Sword Saint's knowledge of the Authority of Gluttony, it is possible that he wasn't actually referring to Subaru but Louis Arneb, who was possessing him at the time. The second time he killed Subaru, Reid added that he "needed" to die, implying he knew about Subaru's connection with the Witch of Envy.

Louis Arneb
Reid killed Louis multiple times while she was possessing Subaru, as he found the latter to be "disgusting". However, due to the first Sword Saint's knowledge of the Authority of Gluttony, it is possible that he was aware of Louis' presence and the insult was actually aimed at her.