The name was coined by the initial developer Yasuo Higa after an Okinawan mystical creature Shisa.

In March 2004, Seasar was re-introduced as light weight dependency injection and AOP container and renamed Seasar2.

In April 2005, Seasar2 obtained assistance from OSCJ.net (Open Source Collaboration Joint Network) and moved out from SourceForge.jp.

Transaction control module (S2Tx), database connection pooling (S2DBCP), and JUnit testing (S2Unit) are all bundled with this core.

From http://ml.seasar.org/archives/seasar-user-en/2010-March/000039.html : Seasar Foundation periodically holds "Karasawagi" conferences around Japan to allow developers and users to talk with each other.