It confused me a little too. It is Darkside.
It's more clear if you look at the part above it.
It's a bit weird to mention Darkside at all in this, since it should be a given as it is with DA/SE, otherwise it should be DA/SE/DS.
Adding DS to everything would be pretty redundant though. DS also isn't actually in the abbreviations so though it's pretty obvious, it was confusing in the context of 'why is it mentioned for this combo if active for all?'.
But yea, I'm pretty sure it's just a non-DA Souleater as they mention Darkside Souleater combo above it in comparison to 'Soul Eater Dark Arts' and Delirium.
