Board Thread:General Discussion/@comment-31059495-20170123120820/@comment-25979511-20170126012759

I'm on my phone which is running slowly so I can't tell if somebody has already replied...

SH is a continuation of the Durarara main story but focuses on new characters. You still see a few old characters like Mikado and Celts, but Izaya is mostly absent, only mentioned (he has his own novels). It is canon, it's written by Narita. I'd suggest you read the main story novels before reading SH though. The anime left a lot out and it could make things confusing at times.