If you're expecting a continuation of Bible Black's story, you might want to look somewhere else for it. Bible Black Only bears little relevance on the plot. In fact, aside from the prelude to a sex scene, it's ALL sex scenes.
I suppose the good thing about this is that if you enjoyed the sex scenes in Bible Black, you're in for a treat. Only two of the main characters are involved in them (Being Takashiro and Saeki), while the rest feature characters that made either a small appearance in Bible Black or were missing entirely.
Only two of the sex scenes seem to anything
to the story, the first involving Takashiro, invoking a flashback to Bible Black Origins and her sole sex scene (I'm sure you'll remember that...).
The second involves only a couple pictures of Saeki, surprisingly as a member of the school's swim team (which I think is a fabrication; there's no indication of this in the game at all).
Don't get me wrong; it's nice to see Saeki in action again, considering how you get only two such scenes in the original, and one of them might turn off most viewers (you know damn well what I'm talking about).
If you need a hentai fix, watch this. If you care about Bible Black's story, maybe watch the first episode. You're given a small Easter egg, and after that....yeah, it's more or less people screwing.