If you're into figure building or collecting, the Wonder Festival at Chiba's Makuhari Messe is worth checking out. The event began back in 1984 with the aim of showcasing and selling model kits from professional figure making companies alongside amateur figure builders – and there are a wide variety of figure types to explore.
Along with the winter event (usually held in February), there is a summertime event that usually takes place in July. Keep an eye on the official event website for scheduling updates closer to the season.