There is a blessing in disguise when Diablo gets transported to another world. There, he actually has a social life. While he does put on a mask to show he's not to be messed with but his genuine kindness attracts the attention and love from Rem and Shera. Later, Diablo marries them.
Rem and Celestine's relationship. Its very reminiscent of a mother caring and worried for her daughter who is adjusting to college life.
Earlier, not having heard about Demon Lords from other worlds, Celestine is initially worried that Diablo might be a Fallen, though Rem refutes this by saying he's had plenty of opportunities to kill her but hasn't, and moreover actually promised to help with her deepest secret when many others have run away. But after seeing him come to her/Rem's aid against Gregore (directly after having wiped out an army of them), reassure the badly-wounded Emile that he was a hero and provide them with a healing potion to use on him, she notes with a subdued, yet genuine awe:
Krebskulm is really such a cutie that Rem and Shera go to huge lengths to protect her.
Even after all the things Alicia put Rem and Klem through, Diablo is unable to hate Alicia because he understands more than anyone what Alicia has to put up with in her life. Instead, he tends to Alicia and asks her to change her ways. Alicia did find her God – a God in a Demon's body.
Rose, Diablo's maid, appears in the new world. Its nice to know that a piece of Diablo's old life lives in this one, and something he cherishes has returned to him.
When Diablo warmly confirms that he's really him - via his Cross Reverie username - Rose nearly breaks into tears and is speechless with joy for several seconds, before warmly greeting him in return. And a bit later, when Rose states that he only used to talk with her before, Diablo gifts her with the first item he ever received, so that Rose may know that she's still adored by him.
In season 2, Horn is getting beaten by some of her former adventuring partners and they're badmouthing Diablo, Rem and Shera. Despite being beaten, Horn stands up to them and tells her tormentors that Diablo is awesome. When her tormentors decide they've had enough of her, Diablo appears, defeats them and gives Horn a piggyback ride back to the festival where Horn reveals that she didn't feel like she belonged with them. Diablo tells her that's stupid and that if no one told her to leave and she didn't want to, she doesn't have to. The whole scene has the feel of a father encouraging his daughter.
