i try to be active and sometimes succeed

I think Casey's a very intense person in the best way posible. She's very loud and feels her emotions very deeply; in the show she has a wild range of facial expresions and emotions

Some think she's chaotic, but I wouldn't exactly frame it that way. I don't think she's chaotic, she's just very intense and has a big flame burning inside her, manifesting in her loudness and expresiveness. However, she's a rule follower and quite strict when it comes to Some stuff

She's a remarcable recruit for the foot; I'm pretty sure the only reason she didn't get promoted was because she failed the one mission in Hot Soup: The Game, not because her lack of skills. She's proficient in at least 5 weapons and very well trained ninja. And, again, a rule follower. When Draxum joins the foot clan, Casey makes a point of listening to her Senseis and doing things by the book; until Draxum joins, she never even considered going against direct instructions/doing things in a way that isnt how theyre "supposed to be". She's loyal to her clan until the clan stops being loyal to her and up until she figures out theres Other Options for her out there

About her putting on a mask, i'm not sure i fully agree. I do agree that she has Some insecurities, with not being promoted, for example. Casey has sacrified almost a decade of her life to the Foot Clan, which hasn't been apreciated or taken into consideration. She wants to make her Senseis proud and she wants to bring forth the return of the Shredder because she believes thats her mission. However, the constant sidelining her, pushing her to the side and not taking her into consideration gets to her. She's probably insecure on her abilities as a ninja because of that, and you can draw parallels to April because of it. In the episode Always Be Brownies, there's an explicit parallel drawn between April and Casey, showing how similar the two girls are. That episode also dwelves into Aprils insecurities over not being good enough (good enough of a saleswoman but also in general (she has some Complexes about not belonging anywhere but thats a story for another day)). Because of this, we can infer Casey feels similarly, also feels like an outsider and also feels like a failure/she's not good enough

The part I disagree with is the masking. I think Casey's as transparent as glass. She's just Like That. Her facial expresions, as mentioned, are wildly diverse and extremely... well, expresive. I dont think she Knows how to mask. If her "confident face" was a mask, I think she would've tried more to keep it up when talking to Splinter in Always Be Brownies. However, if my memory doesnt fail me, she breaks down quite easily upon realizing the limitations of her brownie empire. Casey goes from 0 to 100 because she is someone with unstable emotions who simultaniously feels very very deeply

I want to draw another conection, this time to Donnie. I think that Donnie and Casey are quite similar as characters and have a lot of things in common but I rarely see people discuss or explore this and now that you ask me about my thoughts about her, might as well take the excuse lol

I would have to rewatch the Casey episodes to do a deeper analysis into her behaviour to better discuss this topic, but I would argue that Casey could be autistic coded. Her loudness and tone can be because of lack of awareness on her volume, which can be an autistic trait. She also follows rules and commands strictly, not realizing theres alternative means/alternative paths in life for her, another autistic trait. She can be blunt at times and direct. Some of the way she speaks and carries herself do feel reminiscent of a low masking autistic person- a switch of her not masking to masking could be in Hot Soup: The Game when she first sees Mikey; if i remember the scene correctly theres a Switch in her behaviour in that moment that could be atributed to that. Her feeling big emotions in general and her lack of emotional regulation can also be an autistic trait

Obviously this relates to Donnie because of Donnie's own autism. Donnie masks more than Casey does, but he's not exactly good at it, and he can be loud and excitable too sometimes. Donnie also feels his emotions very strongly and expreses them loudly when he fails to mask. He's insecure over not fitting in with his team and not being good enough and his worth being tied to what he can provide and other fun stuff, which is similar to Casey's own insecurities. Aditionally, both of them are sadistic and very prone to violence, sometimes deadly violence. I think they would be able to relate to each other and bounce off of each others energy in an extremely chaotic and potentially dangerous way to the ones around them

Casey and Donnie friendship is a very interesting one to me and I want to explore it in fics if I get the chance. What i've been writing lately is more Junior and Donnie rather than Casey and Donnie, but i'm one idea away from making an oneshot about the two