The anime's character designer, Kamimura Sachiko, has done a series of BL illustrations featuring basically expies of Daryun and Arslan. She denied any connection but it was pretty much a case of "well, just because one of them looks exactly like Daryun and wears exactly the same outfit, and the other looks exactly like my version of adult Arslan, right down to the clothes, jewelry and weapon, doesn't mean it's them!"
The Stinger art for episode 17 has Arslan in a dress, while a nosebleeding Daryun clutches at his heart. And a nosebleeding Narsus starts drawing.
In the novels' finale, Arslan specifically requests to be buried alongside Daryun with his dying breath.
Elam is extremely devoted to Narsus, and when Alfreed starts making overt moves on Narsus he becomes catty, as though he feels the need to defend his position as being closest to Narsus from the girl who might take him away.
Elam has a more soft and gentle atmosphere around him when he's with or talking to Arslan, and when it is pointed out that Elam acts friendly with Arslan by Gieve, Elam is quick to deny it.
Arslan is shown to worry about whether Elam thinks of him as a friend or not, or even like him, Elam is quick to refute the belief.