Too often, the character of Keiko wa just sorta there: fretting about something, annoyed about something, or bland Stepford-wife furniture. This was partly due to Ms Chao's decision to prioritize family over work, and not be regular cast, which we are bound to admire and respect -- but it evidently hampered the writers from really giving her anything of interest to do.
And then comes this! A Keiko-centered episode, and an utter delight -- and entirely dependent on Chao's performance. This could have been done more politely, but fortunately wasn't. From the very first scene, she takes control of the screen and doesn't let go. Arguably it sorta breaks some of the norms of the show (couldn't O'Brien have told anyone?) -- but so what? TNG and DS9 both had difficulty pursuing real fun, but here they went all in, to the possessed-other story this needed to be.
So: thank you, Rosalind Chao! One of my top 10 DS9 episodes.