V'Atah Kadosh after the M'gillah: Kitzur S"A 141:4

[Richard]

The Kitzur SA claims v'atah Kadosh commes from Psalm 22 and thereby alludes to Esther as Per a Midrash on verse 22:3

Yet we also say V'Atah Kadosh after M'gillas Eichah on the evening of the 9th of Av. And so it seems that this is the structure of Ma'ariv for these 2 occasions, namely M'gillah, followed by v'Atah Kadosh followed by Kaddish.
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Shalom and Best Regards,
RRW

MISTAKES are always forgivable
If you have the courage to admit them.