Arakawa was Uesugi Kenshin's Kagemusha (double) during the 4th battle of Kawanakajima. During the battle, Takeda Shingen and Kenshin purportedly fought in one-on-one combat, however, there is a evidence that the man who attacked Takeda Shingen was not, in fact, Uesugi Kenshin at all, but his Kagemusha, Arakawa Izu no Kami. According to the Kenshin Nenpu (Kenshin Chronological Record), Arakawa, who was dressed as Kenshin, rode at Shingen and attacked. Shingen was unable to draw his sword, and so blocked with his war fan. Hara Ôsumi no Kami ran to Shingen's aid, and drove off the mounted warrior.
To further confuse the issue, according to the Hokuetsu Gunki, at a later date after the battle, Shingen recieved a visit from a monk by the name of Tenkai who would later become an advisor to Tokugawa Ieyasu. Tenkai would tell Ieyasu that Shingen told him during thier meeting that "the man who crossed swords with Kenshin that day was not me, but someone who looked like me".
So it is possible that the "famous" clash between Shingen and Kenshin during the 4th battle of Kawanakajima was in fact a class between thier respective Kagemusha instead.