Adeleine as a character have been on my mind as of late, so I feel like sharing a mix of general and au specific headcanons for her!
-She's extremely kind. She'll be there if you need someone to talk and always has something kind to say to those who are kind to her.
-She's very attentive, noticing a lot of small details that nobody else would normally.
-Adeleine prefers the simple and calmer moments in life, preferring to take life slow and enjoy things in the current moment
-She's a pretty patient person, but will get very angry if pushed to her limit
-Adeleine manages to get along with nearly everyone. The only reason she wouldn't get along with you if you're being constantly rude to her or her friends, or are just being a bad person in general
-On that note, Adeleine can't stand chaos or people who try to bring chaos into the lives of others
-She doesn't like to pick fights if it's not necessary. But if she must fight, then she'll fight!
-Loves spending time with her friends, whether it be joining them on an adventure or drawing with them
-Definitely has a good sense of humor, whether it be a good joke or lightly teasing a friend
-Has a very good singing voice! Loves to hum a tune or song whenever she's painting or doing something else. She also will sometimes sing a sentence when very excited
-She tries to be a very logical person, but sometimes she can't help but let her heart and morals do the thinking for her
-Can be shy and reserved, especially when meeting new people, but once she gets to know you, she's very energetic and bubbly
-Kirby, Bandee, and Ribbon are her closest friends. More often than not, they're by her side.
-Her and Gooey have been getting to know each other better after Star Allies, and the two are becoming closer friends now!
-The Animal buddies are also friends she's on good terms with. They'll often stop by and check in with her or hang out if she's nearby them
-Her and Dedede are very good friends. Adeleine viewing him like an older brother and Dedede of course being protective towards the kid
-She and Meta Knight don't know each other too well, but she's been making an effort to try and know him better
-She's on decent to good terms with the other dream friends/Kirby's friends, with most of her dyanmics ranging from "familiar with each other" to "good friends"
-Marx and Zan are probably the two dream friends she doesn't get along with. Marx's chaotic and prankster nature can often get on Adeleine's nerves, especially with how over the top his pranks can be at times. And Marx knows this and intentionally likes to mess with her (even if it ends with Adeleine chasing him down with her paintbrush). And Zan is just very rude to her, so she prefers to keep her distance from Zan if she can help it.
-She actually stayed behind on Ripple Star after K64 for art studying, which is when she also developed her friendship with Ribbon
-The aforementioned Kirby, Bandee, and Ribbon like to look up to Adeleine at times, seeing her sort of like a group leader in moments they don't know something
-Adeleine tends to give a lot of decently solid advice, always wanting to help out however she can (though sometimes it can be a bit overbearing, but she tries her best regardless)
-I like to headcanon my Adeleine as Aroace (I also view game Adeleine as Aroace as well, but it's outright canon in my au she's Aroace)
-She doesn't tend to get frequent haircuts, often letting her hair grow out and keeping most of it tucked under her beret (until it becomes too much and must be cut)
-She tends to prefer long sleeve outfits due to style and warmth
-She has a full name: Adeleine Renoir Thorella
-Her brush was a gift from her parents! They gave it to her before she set off to Dreamland to study art for the first time, both for studying and defense purposes
-Said brush is also powered by Adeleine's creative mind and caring heart, which allows her to make whatever she paints come to life. It can also allow her to unleash pretty powerful paint based attacks, but she only uses that power when she deems necessary
-I like to imagine she tends to paint a lot of faces from the Dark Matter trilogy, mostly because those were some of the first people she met and being good friends with them. They mean a lot to her
-I already mentioned she doesn't like chaos, but in my au, she can get quite fired up/angry if you're being rude or chaotic to her or those she cares about
-I mentioned she prefers not to fight when not necessary, but she has been taking more opportunities to train on her own or with others to better defend herself or improve her attacks whenever she has to get into a battle. Be it with friends or trainers, as long as she's improving, Adeleine's willing to train and improve her fighting skills for the future!
-In regards to her paintbrush and family, I personally like to image they're still out there, and Adeleine spends time with them whenever she's not on Popstar
-On that note, since Adeleine doesn't live on Popstar, I imagine she stays at a small inn at Dreamland whenever she's visiting
-She does eventually move to Popstar by the way. I feel like she's grown such an attachment to the planet and its people that she wishes to make Popstar her new home
-Some of the monsters from the anime are actually her creations! More specifically, ocs she made in a sketchbook. Though they're not very malicious or violent like they are in the anime (Also she's slightly hesitant to paint them to life, due to a mix of slight embarrassment and still trying to figure their stories out)
That's all I have for now. Adeleine's a fun character that I've grown attached to as I've been developing things regarding her in my au. I hope you enjoy these headcanons!