UML modeling tool Jude is a popular software design tool amongst Japanese developers.
A free version of Jude has a capability to write all diagrams of UML (class, robustness, usecass, activity, sequence, collaboration, component, state-chart, and deployment). A professional version costs 29400yen ($275) and supports ER diagram, Dataflow diagram, and Mindmap.
Kenji Hiranabe is the guy who created Jude. He is a popular evangelist of Software methodologies in Japan.
Jude has a beautiful anti-aliased graphs, and sophisticated user-interface. It has an English, Spanish, Portguese, and Chinese version too. It’s worth a try.