The Japan international previously wore the Dortmund jersey between 2010 and 2012 before leaving the club for Manchester United.
He failed to make an impact at Old Trafford, though, and has now returned to the club where he rose to prominence in Europe, much to the delight of BVB's fans.
Over 5000 jerseys with Kagawa's name on it have been sold since Dortmund announced the signing of the attacking midfielder and the club have little doubt the 25-year-old's return will benefit the commercially.
"The transfer of Kagawa plays right into Dortmund's hands when it comes to merchandise," Cramer was quoted as saying by Bild.
"Kagawa is a huge boost for us in Japan and the rest of Asia. This gives us a push in the right direction.
Kagawa won two Bundesliga titles and the DFB-Pokal during his first spell at Dortmund.