>>50152175As another matter of frame, we spend almost a minute in closeups of Ash and Serena's faces. EVERYTHING ELSE is excluded. Their eyes are specially detailed, communicating emotion. The soundtrack is Serena’s theme from the game, which i salso na emotional song. They don't say goodbye to each other: they inform each other as to what they are doing and wish each other good luck. Because, again, the focus is on the meeting, not the goodbye.
And, finally, once they depart, we stay with Serena (and, in universe, Serena remains there for as long as it takes for the sun to set). Compare with the DP finale, which is the closest to this in terms of setting: as soon as Ash's boat departs, we cut to Dawn hugging Piplup, and then smash to black, because once the separation is done, there is nothing else of import to show. On the other hand, PM considered it important enough to show Serena contemplating the sea.
None of those things was ever done with a past companion, or at all, in the series so far.