Roswaal L Mathers/Relationships

Echidna
At some point 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 like the fact that he never cared for her except for Echidna. This changes 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 former died of unknown causes and he immediately suspected that Subaru is responsible (he was even prepared to kill him, much like Ram).

Emilia
Emilia's benefactor and backer in her bid to acquire the throne. He's considered an odd lord, especially due to his fondness for demi-humans like her to the point where he would hire them. In truth, he is only actually using her to control Subaru and coerce him into using Return by Death to fulfill his ambition of reviving his late master through the wits of his Gospel. To do so, he needs a guaranteed way to put Emilia on the throne because he has no faith in Emilia's resolve to overcome her past and deeply-rooted hatred of the Witch of Envy. However, with the encouragement and support of Subaru and several others, Emilia shatters his expectations by passing all 3 of Echidna's trials. He is then forced into backing her earnestly.

Natsuki Subaru
When they first met, Roswaal appeared to be genuinely grateful for Subaru rescuing Emilia's insignia, even offering him anything he wants as gratitude. He appears to be rather friendly to the young boy. However, Roswaal is 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 have placed a bet, which he lost (although he will force Subaru to use Return By Death, should he make a mistake).

Hector
At some point in the past, Hector pursued 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.