A little rough around the edges, but I'm not very good at this kind of thing. Hopeful for the best, though!
The chair itself could be a reward for showing up during the start of the event period. Backstory could either have it as a thank you gift from Maple Admin, or from Cassandra. For the latter, she had it commissioned ten years ago because she had foreseen the coming of the Fifth Job advancement in her crystal ball. Some item descriptions I had in mind:
"This high-tech chair was created to celebrate the V update."
"This chair depicts the high octane journey to level 200, where Fifth Job advancements are now possible."
"A chair made in celebration of the V update, which commemorates the launch of the Fifth Job advancement."
"Go from 1 to 200 in a flash with this celebratory V chair."
"Get into the spirit of V with this [chair name] chair, made to celebrate a fantastic event loved by many. "
It's not the best, but I'm sure the art team could make it awesome. Thank you for your time!