One of mari’s quirks is that when she s bored she’ll draw on anything, she won’t hesitate to draw on the table, or chair, or the wall (if it wasn’t for the vandalism charges 😞)
I’m not sure about kel since I’ve focused more on Mari recently but I’d say something like constantly checking on everyone’s social status in his diary (he’s insecure about being popular and is also a perfectionist but in the gifted kid kind where that all falls apart after 7th grade :’<)