Damn, all that amazing buildup for either the ending where they get together or he commits suicide, complete with Tsunami at the climax to mirror Sato's intensity (and presumably Isobe's intensity, him erasing his computer = erasing his history in preparation for suicide)
... and then out of nowhere they don't do EITHER of these endings and go off on another path! THAT was a big let down! Like seeing a huge firework being built that never goes off.
But I get it. Two other users have pointed out the narration's style and it fits perfectly. Life is like the sea, the waves always bringing up a mix of people, emotions, situations that would normally never meet. Then the waves pull back, and what was mixed now gets separated, and new different mixtures are made when the next wave comes in (like the mixes Sato made with Masami, then Isobe, then Otsu).
The artist was slick with the panels showing the ebb & flow of the wave going in/ocean, then a person or something, then a wave going out/ocean again. Later on you'll see this same ebb & flow happening every other panel in the same fashion for other besides waves (like frame of Sato's confession letter, then a frame of Isobe, then back to Sato's letter).
And... This big let down was all done on purpose!! The "waves" and panels may bring together some interesting mixtures like a hat blown by the wind, a blown out firework, or Sato+Isobe. You'll never know what you'll find (brought together by the sea) , but if you don't have any expectation then you won't get disappointed by what you'll find... The same way I was disappointed in the resolution of Sato+Isobe, but had I come in on an "earlier wave" the story would've been disappointed in would've been about Sato+Masaki.
Damn clever writing. The disappointment was an intended feature, not a mistake.