This is a renovation project of the entire stadium area commemorating the Seibu Lions' 40th Anniversary. The concept of DOME + BALLPARK (baseball park) was achieved as this dome stadium surrounded by greenery has no walls. In the station plaza and around the dome, flat decks were built over the hilly terrain using brick arches as a motif. They allow for many stores that welcome visitors to the stadium. Inside the dome, underneath the area behind the plate was dug down to the playing field level to create a space for spectators that is closest to the players and has the best view. The players' dormitory and indoor practice facility were reorganized into one building and connected to the outdoor practice field by an exclusive corridor to create an ideal practice environment. During the 3.5 years of the project, a total of 25 buildings were newly constructed or renovated. The project has improved the value of live spectating and team development, achieving a stadium where both visitors and players could enjoy.