I would hazard a guess at Black star, Death the Kid, Maka, and Definitely Patty and Lizzy (Death the Kid's weapons) and just because he is a demanding little prick Excalibur...i mean how do we know that one of his 1000 provisions isn't they have to treat him like their baby for X hours/days at a time

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While there are certainly quite a few characters I'd like to see in diapers, the question of who would actually be into that kind of thing is a lot trickier. That being said, I think Sakaki from Azumanga Daioh fits the bill. Besides a fondness of things small and cute she's also shown a desire that she could be that way too. Doesn't necessarily mean she'd want to try out acting like a baby, but it's a possibility.
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Oh My Frelling... Winnie Cooper-sama, that transcript was AWESOME!!

I'm surprised I haven't seen this one yet mentioned, but Amy from Sailor Moon; fighting yomas and studying hard to be a doctor, she must need a good stress reliever. It wouldn't be to far a stretch of the imagination that, given her mother is also a doctor, she couldn't have gotten into supplies and such.

I'd like to see Naruto diapered, Kira Yamato from Gundam Seed, Ichigo from bleach, female wise Sakura from Naruto, Ed from Full metal alchemist, Maybe Rangiku from bleach, Kirito from SAO, and Asuna as well, Natsu, Erza, Lucy from Fairy Tail. The list goes on

Tayuya from naruto

She's feisty and defensive wich would say shed have something to hide, with her attitude she'd make a great abdl in secret to let her sweet and innocent side out in secret

Could yo please provide a link because google isn't much help...

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See, I just don't see "needing stress relief and has access to medical supplies" as a good enough reason to see a character as ABDL. More than good enough to write a fic/draw a pic about it, sure, but not as a serious argument for the character actually being that way. If it was just a matter of stress relief then Minako/Venus might be the better pick, as she not only had to put up with the stress of being a solo Sailor for a year, but she's also constantly frustrated in her love life as well. And as she's supposedly the goddess of love it could be argued she's also the goddess of kink (come on, one of her attacks is "Love-Me Chain" which she uses to whip people).

That being said there is a different argument that could be given to Ami wearing a diaper occasionally. In the manga during the Black Moon arc it's revealed that when Jupiter gets ill she also gives off electricity, shocking people who touch her (not dangerously so, but more than just a bit static-y). The explanation she gives for this is it's a side effect of her losing a bit of control over her electric magic while ill. This could then be extended to the others with their powers as well. And as Ami has water/ice powers, she might feel really cold and have trouble controlling her "water".
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I'd say Erina and Megumi from Shokugeki no Soma definitely! They're the first off the top of my head but I'd also include Sakura and Hinata from Naruto, Vivi and Rebecca from One Piece, Lucy and Levy and Mirajane from Fairy Tail, Chiyo and Hana from Prison School, and Alex from GANGSTA

I also found out another one thanks to my BF. Kenichi from Kenichi world's strongest desciple. He goes through HELL AND BACK just to be able to defend himself and those he cares for. (he literally dies like 10 times from training and is brought back to life from one of his masters restarting his heart.) and I think MAYBE Apachai from that series as well. He is just so innocent and pure that despite being the worlds deadliest Muy-Tai fighter I could EASILY see him wearing them and being babyish from time to time becuase he would find it fun and cute.

also Aladdin and Ali Baba from Magi