This historical site is a collective tomb of 54 sailors from Ryuku (today’s Okinawa), killed by Paiwan aborigines in 1871. The incident subsequently ignited the battle between the Japanese and the Paiwan in Shihmen in 1874. Note that the first three characters on the stele, literally saying 'Greater Japan', have been blotted out.
It's located just off County Rd 199 near the Km36 mark (look for the Japanese-style stone lantern on the roadside)