the chibi marumi is probably from a scene in box r showing the ditzziness of chitose (marumi role).
the japanese words for "abdominal breathing" (fukushiki kokyuu) and "marriage ceremony" (kekkon shiki) both have the word "shiki". In the manga, "abdominal breathing" was written in hiragana, which implies chitose isn't familiar with the word and came to her definition of abdominal breathing based on the similarities in the sounds of the words.