MapleStory has a crossover with Attack on Titan that brings Titans from the anime series into MapleStory's events. A portal in the MapleStory world lets characters level 30 and above into the world of Attack on Titan.
The MapleStory 1st Festival will have live performances by Sistar and Girl's Day (pictured). Spiral Cats, the Korean cosplay team that did the Sarah Kerrigan cosplay for Starcraft II: Heart of the Swarm, will also be at the event.