>>537983134
it actually procs the same place as seiun sky's, and her's is amazing, but in the case of end closers and letspump, you already have straightaway spurt getting helping, so when your end reaches the corner they don't have much more to gain.
Even if you do get it to activate, it only gains you half a length. Straightaway Spurt gains you 3 lengths. Without Straightaway Spurt, Pump would gain you a full length.

Looking at it, Seiun's isn't that strong either for this CM. It's not nothing, but a front has to rely on a lot more than seiun's unique to win this one. picrel includes seiun herself using it. inherited would be identical to the letspump graph.