Ugh. I hate "it's magic!" without any kind of explanation. I think it's a cop-out, honestly.<br/><br/>I can see there being a kickstart, that would make sense, particularly if they've fed from their mother in utero. I have a hard time stretching it to make sense, given that you need a constant source of energy to maintain growth, but with a decent enough explanation, I could swallow it, I guess. I'm just not sure how it would last a century, is all.<br/><br/>Breasts wouldn't be part of their demonic form, though, if it was just used as a lure. Their human form, absolutely, but it wouldn't be necessary in their demon forms, since they're just for visual appeal. If we use breasts as an indicator for... "magic" or whatever (which I'm still not sold on for them in general), then men have none. Due to... you know... no breasts. Or, we could argue that because they have nipples, they have breasts, they're just much smaller, which means every incubus is automatically inferior to any succubus, regardless of age, experience or bloodline. I don't think that's a viable option without essentially castrating half the cast. That isn't greatly fair.<br/><br/>If someone could come up with a believable explanation, I'm willing to talk it out. I'm just not convinced by those ones. They seem kinda like they're off-hand excuses to fit fantasy than explanations to support plausibility.