So Fishe is the metaphor for Marisa`s happiness? How does this all fits in the original theory of Fishe? What do Sakuya and Cirno have to do with everything?
Now if we look at the words Sakuya giving Cirno the fishe under this new angle, we are able to uncover the, perhaps, truth behind it.
Sakuya`s role is fairly vague and uncertain, but at the very least we can deduct that she is somehow connected to delivering fishe to someone, in this case Cirno who will most likely consume it judging by her almost animalistic hunger showing in her face. Can she actually devour happines of living things? Perhaps she just selfishly hoard it for herself? In my opinion, in first case the story of this 2hu trio could be an allegory of abusive family with Cirno acting as the sadistic Father who oppress poor Marisa ravaging her cheerfulness, and Sakuya acting as the mother, enabling her spouse (this is where giving the fishe part comes into play) and taking more passive approach.
However if we take the second approach with Hoarder-Cirno it could also be interpreted as NTR love triangle of sorts.
Although, perhaps, the truth is still out there.