KOSEI MARU is a very apt choice for confusion. On Jentschura, Jung, Mickel "Warships of the IJN 1869-1945" I find the following five ships by that same name:

K.M. built 1915, 1026 grt, requisitioned as a netlayer 1941, subsequently returned to original owners.
K.M. naval collier, 6667 grt, diesel engines, built 1933, sunk 10.3.1942 in Cam Ranh Bay by mine.
Miscellaneous mercantile auxiliary vessels:
K.M. ex NARENTA ex NEGANTI, victualling stores ship, 8237 grt, turbine refrigerator ship built 1919, requisitioned 194.., returned early 1943, sunk 8.4.1943 NW of Truk by USS TUNNY.
K.M. ex MEIJI MARU, transport, 2205 grt steamer built 1924, requisitioned 194.., sunk 27.1.1944 S of Formosa by USS THRESHER.
K.M. transport, 3551 grt steamer built 1937, requisitioned 194.., sunk 11.11.1943 E of the Nansei Shoto by USS SARGO.

(more to follow)