Roswaal L Mathers/Relationships

Echidna
Somewhere in the past, while Echidna was alive, she took Roswaal as her apprentice. After her death, Roswaal became obsessed with reviving her and killing Volcanica.

Beatrice
Being an acquaintance of his master Echidna, Beatrice and Roswaal simply maintain respect towards each other, however, Beatrice didn't tolerate to see how he never cared for her except for Echidna. That fact changed over time after the events at the Sanctuary.

Ram
Roswaal took in Ram and Rem under his wing and is shown to deeply care for their well-beings, using the former as an informant on matters. Despite this, he has no qualms on sacrificing her to meets his goals as shown in Arc 4, where he kills Garfiel, despite Ram being in the way in one loop.

Rem
Roswaal took Rem and Ram under his wing and was shown to deeply care for them, as seen when the fomer died of unknown causes and immediately suspected Subaru for the situation (he was prepared to kill him, much like Ram).

Natsuki Subaru
When they first met, Roswaal appeared to be genuinely grateful for Subaru rescuing Emilia's insignia, even offering him anything he wanted as gratitude. He appears to be rather friendly to the young boy, however Roswaal was more than prepared to kill Subaru in one of the loops, connecting him to be the cause of Rem's unknown death.

In Arc 4, their relationship became rather antagonistic (i.e. giving Subaru half-truths or intentionally throwing monkey wrenches in the latter's plan). Roswaal becomes aware of Subaru's "Return by Death" and later admits that he's molding Subaru to become like himself (acting on his own desires rather than waste time saving someone's life). By the climax of said Arc, Roswaal and Subaru placed a bet, which he lost (although he will force Subaru to Return By Death, should he make a mistake).

Hector
Somewhere in the past, Hector was pursuing Echidna and Roswaal tried to beat him in a fight, but he ended up badly wounded. Since then, Hector became his rival. Also, Roswaal started to wear clothes and talk like him.