FF VN Concept

I saw this set of images posted on hitomi.la, and while it's definitely just something that will irritate me, I couldn't let Issei having a sister go. Adding new characters is fine for a fan-fic but i feel it stretches things too far when you add a character that cannot exist for a reason explained in the actual series (Issei's parents struggled to have children to begin with and were so happy they were even able to have Issei, that they didn't care when they found out he had been turned not only into a demon, but his body was reconstructed out of dragon flesh). Sorry for the rant, just a pet peeve.