I’m kinda surprised I haven’t drawn Delia more than I have. So the joke about Oak fucking Ash’s mom while he’s out adventuring is an old one, since the anime tends to have Oak appear alongside her whenever Ash sees his mom. It’s probably unintentional, but they do come across a bit like a couple. I’ve always thought it was funny to re-purpose Oak’s lines from the games (that was the premise of the only other time I’ve drawn him, after all), so I worked that into this answer.
