I bet Haru is the one who put that mug on Midori's Bag....Just a daily reminder that she will come back which reminds me of Midori's line: "I never did have anything that could give form to my memories with Tsumugi chan"
Is there actual proof that Midori's feeling for Tsumugi is in the romantic form...cause I think it's not like that. What I've learned is Tsumugi and Haro is the one who is in love with Midori.