This is my hypothesis.
I will make a reference for these two series: the Kakegurui Twin series but also in the Kakegurui series
I believe that Kaede Manyuda entered the student council at/through Aoi Mibuomi's recommendation, just as Sumeragi Itsuki entered the student council through Kaede Manyuda's recommendation.
Aoi Mibuomi who was the treasurer of the council in the Kakegurui Twin series, and I think that Kaede Manyuda, when he was in the first year, did not have any position in the student council.
And it would be really interesting that in the Kakegurui manga series or in the Kakegurui Twin manga series, we would be offered a kind of memory of Kaede Manyuda with Aoi Mibuomi where the following is present:
Aoi Mibuomi (to Kaede Manyuda): In a few days, I will graduate, so I offer you the position of student council treasurer.
Kaede Manyuda(to Aoi Mibuomi): Thank you senpai
Aoi Mibuomi (to Kaede Manyuda): One more thing Manyuda-san, if you end up somehow using a woman, like a pawn on a chessboard, know that sooner or later,you will end up having her part of,sweet,her revenge.
And if that woman intends to help you,after taking revenge on you, know that she is your soulmate.
Kaede Manyuda (to Aoi Mibuomi): Senpai, if you keep joking, know that I'm leaving.