I'm only a beginner but this is my attempt at a solution.
I think the only place that will allow blacks group to grasp for life is at .
If is followed by and , in order to protect whites investment in the corner, then extends down the right side and can either be sealed by and but will allow black's group to live.
While this contains black from spreading down the side but black can now attack the corner preventing white from gaining enough eyespace to live.
Either way black isn't in as strong a position as he could've been without the hane. He has the chance to recover the corner but would lose influence towards the right side and center.
White Move: "a" for seki, "b" for Ko fight?
tapir: White a may still be ko. And most probably is, since after white a, black connecting, white needs another move to make the eye and the ko is then direct for black (and two-step for white) - which for the black player will be most often better than playing b for a seki. Since white reads the same, she should start the ko when black connects after a or at least not taking away her own liberties for an unlikely seki.