Possible idea plot twist... Requesting feedback

Okay... so I have the main prequel storyline going for my OT (the never seen, vaguely mentioned only once father of Ash)...that unto itself is it's own story. But I keep getting this nagging plotbunny for a separate story set years after most of what happened in the anime... well, happened (of course, that being, time is really vaguely relative)...

I'm sure there are others out there that have/had an OT/OC be a sibling of Ash, though I personally have not looked very far or very hard... I have a possible story for one of my own. My main question is, would it sound better to have in a story (set several years after the one I'm writing now) that the sibling was related by blood (as in the Ketchums have a baby the 'natural' way) or to adopt? I'm kinda leaning towards adoption as I have something that I could possibly use towards the begining of it all, but if adoption doesn't really work well, then what I wrote will either 1 collect dust until the day I trash it or 2 collect dust until I can figure out how to use it elsewhere.

I even have the gender and the name (cliche/bad pun intended) all picked out... but I'm not sure how anyone would really react to it...

Plot hole people who do this never answer:

If the sibling is older, then we should have heard about him/her in canon unless you have a really good reason for why Mrs. Ketchum decides not to mention to Ash a long-lost sibling. On top of that, you'll need a good reason for getting rid of said sibling without stepping on the fact that Mrs. Ketchum isn't that old of a mother (i.e., trainer's license excuse is kinda out) or the fact that Mrs. Ketchum still has Ash.

If the sibling is younger, then that's less of a problem, but it still depends on how far into the future (with the current canon being the "present") we're talking here.

So, most likely, adoption's probably your best option to avoid screwing around too much with ages.

Yeah, I forgot to mention the sibling would be younger by at least 5 - 7 years at the bare minimum.

If I do go with adoption (the events leading up to it isn't going to be mentioned at the moment due to the fact that I'm not 100% sure I like what I wrote), the Ketchums foster a girl named Aisha. This part starts going into the bad pun/cliche naming thing. When they decide to adopt her, she decides that she wants both of their last names as her last name (In the story I'm writing at the moment, since it's pre-Delia getting married to Ash's father, I've went and given her the maiden name of Godda). Aisha also has the nickname of Ai. Now for the most part, I don't have a major plot to have her grow from being adopted to the point where she grows up and gets married herself (and I'd want to finish writing the story I have first anyway)... But if/when Ai gets married, her full name (going with her nickname) would be (highlight to see it) Ai Godda-Ketchum Awl (I gotta catch 'em all) the mother of all groaning/on-running puns...

Wow. Talk about the mother of all bad puns. But I like puns, so wheee!!!
Interesting idea...Well...I dunno what else there is I can say. Just I'd like to see this. xDDD

I'm loving that pun, but you have to keep in mind that if you indeed use a name like that, no-one will take the fic very seriously. You have to keep your humoristic approach.
Just a reminder here.

Please, proceed.

Yeah... I realize that if I do stick with the name and all, that the fanfic won't be taken very seriously... other than some serious business at the beginning, I don't think there'd be much seriousness within the storyline (could be wrong on that since I still don't have much of anything to go on). But eh, why leave all the humor to the parody fics? :D