As the mushroom was an ascomycetous fungi with roots in the soil, and the octopus was a cephalopodan mollusk forced to live its life in a blurry blue prison, the two could see each other only if the octopus climbed onto a rock near the surface and straightened its tentacles, lifting its head outside of the water and gargling short phrases at the mushroom, who would answer in a sweet voice.
The octopus fell in love with the mushroom, and the mushroom fell in love with the octopus. On any day you could the impassioned gargling of the octopus followed in quick succession by the dulcet tones of the mushroom's speaking voice. Although they never got to be physically close to each other, the two accepted this and tried to make the best of things.
Millennia passed, and their love flourished. To pass time, the mushroom enjoyed knitting thick sweaters, watching cooking shows, and thinking about moss. The octopus worked on crossword puzzles and busied itself writing books on existential philosophy. But even when knitting or pondering the essence of existence, the two thought of one another incessantly.
On a lukewarm day breezy enough to make the mushroom sway, a large wave came over the sea. The octopus, who was busy thinking up a nine-letter word for "love", was grabbed by the large blue hand of a wave and smashed onto the shore, eight limbs tangling into a sorry ball. The octopod came to after a decade to find the mushroom gone. In its place was a bright young patch of moss. "Where is the mushroom?" gargled the octopus to the shimmering green moss. "It decomposed into the soil and from that soil, we grew."
To the left of the patch of moss was a sweater, and protruding from the sweater were eight thick orange argyle sleeves. The octopus crawled into it and cried, wiping its tears on the diamond pattern the mushroom had so lovingly knit. His eyes filling with tears, the octopus filled out the space in the crossword puzzle he had been working on. Knowing full well that the answer was "affection", the octopus penciled in "mushroom", leaving a space for his heart to sit and mourn.