The screenwriter said the show feels like a "new way of telling these stories".
"We've had stories before that have deaf characters in them, but having a group of deaf actors and deaf characters and hearing characters who use sign language as well is unusual," he said.
"Scenes with two deaf characters conversing one another together in sign language and subtitles for hearing viewers – I think that's groundbreaking maybe."
Mr Mager said he is "really proud" of the script, which he said he wrote for himself.
"I wanted to write something thrilling and appealing that just so happened to include a deaf person who uses sign language," he added.
Bristol actor and radio BBC Radio Bristol presenter Joe Sims, who also stars in Reunion, said he is "absolutely delighted" to be part of the show.
"Billy is a good friend of mine. I read it [his script] and it was absolutely incredible," he said.
The four-part series aired on Monday evening and can be watched on the BBC iPlayer.
