User blog comment:B214/Volume 23 discussion blog/@comment-201.19.100.21-20170409030136/@comment-3965848-20170409202905

@Ultimate Pawn Correction: Onee and Aneki means older sister while Onii and Aniki means older brother. Issei did think of Asia as a sister until V6, although even within that time he still had erotic thoughts towards her and since his parents took her in she's kinda his step-sister too, so not that different.

When you think about it there're other similarities between Shinmai and DxD: The MC has brown hair and has a gauntlet/sword weapon (Issei) the main girl Mio has red hair, incredible red-ish demonic power and is a demon with notable lineage (Rias) The Succubus Maria has white hair, immense strength an older sister and is a loli (Koneko)

Interestingly, while Basara isn't a perv, the loli is a huge one which he gets mad about, and he's the master instead of the demon girl, so a bit of role reversal.

P.S: I think he has sex with Mio in V10, check illustrations.