I believe An Se-young's greatest strength is her high clear

She often struggles in international competitions due to air conditioning drafts,
and that is because it affects the accuracy of her high clears.
If she can flick high clears to the far corners and hit ten more to the same spot,
but then they keep coming back and forth, it's like being put through grueling drills.
When she sends a high clear very accurately as a diagonal smash,
and then receives it with a slide and a hair-pin, the opponent has to run from end to end to return it, which drains their stamina.
If she succeeded frequently, they wouldn't have to run as much, but if they keep having to return them, they have no choice but to run even if they can't reach them; eventually, their stamina is exhausted.
Since her high clears are near flawless and she can return diagonal smashes,
there is simply no way to win against her.