I just reread part of it and realized, Reimeilia already forsaw that youmu would win, which is why she was snickering, because her ability probably doesnt allow her to literally change the outcome, but for her to prepare to deny this outcome. Is yuyuko the mastermind behind all this? Perhaps she lost on purpose, as to get youmu to play. I mean, why wage so much for majong, (not with common sense, but even so, winning here doesnt actually seem to have any merit besides for the sake of it, so a contract cant really be made under the foundation of a majong game here), if danmaku still exists in this world and is a more definite mean to decide.