Megilas Esther
Begins and ends with the letter vav.
Rashi on Esther too.
Vav on both ends.
Vav is the letter of emes, everlasting reality.
Megilas Esther and Purim will never fade away.
Haman certainly does.
Except for the vav in the nun of his name.
The height of Purim avoda is to isolate that vav, and expand it to eternity.