The theme is Takeda Shingen, a representative legendary Sengoku warlord, and inspiration was taken from his nickname, ``Tiger of Kai.''
Paired with Echigo's dragon, Uesugi Kenshin, this work is an optical camouflage that changes appearance depending on the light and angle.

One of Koga's most popular works is Hooyoroi Hai.
It uses the unusual helmets of Sengoku warlords as a motif to express people's way of life and spirit.

Tea ceremony is a Japanese comprehensive art that developed as a form of education for the samurai class. Sake vessels developed as kaiseki vessels based on this lineage.
Koga describes this work as ``a porcelain cup in the form of a cheek armor, which was naturally derived from the close connection between tea ceremony, Sengoku period military commanders, and crafts, especially pottery.''