maybe pisu is aimi? which is why the text said "i seemed to have died that day" which sounds like she is still alive observing from somewhere, then the panel goes to a picture of an open eye then pisu under the table.
chapter 20 as well. you can see pisu's eye reflected in aimi's left eye when she woke up.
going back to chapter 21 as well, its already giving hints as to what happened to flare on previous time loops. gahd this manga really makes me feel so alive.