I am not sure about this. I have a strong feeling that Shimamura will be the aggressive one once they're in a relationship. She's a top, I bet. Lol
You know I actually feel the opposite. To date the dynamic has always been "Shimamura defaults into a doting big sister type and Adachi is the fumbling backwards introvert" but now that Adachi is starting to come into her own, and make strides toward betterment on a personal as well as relationship level, I feel like the roles will eventually reverse.
Adachi is going to be the doting, confident, "lemme be your reliable big-sister-type" one, and Shimamura is eventually gonna let herself be the one spoiled and coddled a bit. I mean, Shima has already demonstrated several times both in action and words that she really likes Adachi's hizamakura. And I'm okay with that because that idea screams "FREAKING ADORABLE" to me--calm and content Adachi petting relaxed and happy Shimamura's hair while she's all curled up with her head in her lap.
FREAKING ADORABLE I say.