In a potentially more erotic route, I'd make Kon and Bianca's demon baby human-looking, but packing evil eyes and a massive cock that he inherited from Kon. As hentai usually goes, the baby would develop quickly, eventually kill off Kon, make his own mother Bianca into his bride, and rule the kingdom as the anti-christ.
^ As someone who only knows the pr0n, I think Bianca is the giga-womb who gives birth to the "Hero" of DQ5. She's the titular "Heavenly Bride", and she gets kidnapped by Kon and taken to a tower of demons in the story, which you then save her from in typical JRPG fashion. I think she's already a mother when she gets kidnapped. The event basically boils down to a hot Milf becoming the prisoner of a giant (naked) horseman for weeks... so even the most basic of smut-minded individuals can connect those hentai dots.