It seems that the concept of teshuvah is missing from the story of purim.
although the megiilah does say:
וּבְכׇל־מְדִינָה וּמְדִינָה מְקוֹם אֲשֶׁר דְּבַר־הַמֶּלֶךְ וְדָתוֹ מַגִּיעַ אֵבֶל גָּדוֹל לַיְּהוּדִים וְצוֹם וּבְכִי וּמִסְפֵּד שַׂק וָאֵפֶר יֻצַּע לָרַבִּים (Also, in every province that the king’s command and decree reached, there was great mourning among the Jews, with fasting, weeping, and wailing, and everybody lay in sackcloth and ashes.)
This passuk seemingly shows that the jewish people were simply concerned and fearful about the actual predicament which they found themselves in.
There does not seem to be any mention about doing teshuvah or repenting to God to save them.
The Gemara Megillah 14a makes a reference to the teshuvah of the jews, and this teshuvah seems to be in a manner of Teshuvah M'yirah.
I am most interested in finding out what the teshuvah was attoning for, did they recognize their error of attending the feast? Was there another major sin committed that they were attoning for? Furthermore, the comparison with Yom Kippur seems to associate Purim with Teshuvah, but it seems to be a difficult topic to pinpoint.
Any help with this is very appreciated. Can anyone point me in the direction to delve deeper into this topic.