Cika jumla mai zuwa: Baya ga Associationungiyar Greater Asia, Matsui ya kuma yi aiki a duk lokacin yaƙin a matsayin Shugaban Associationungiyar don Tsarin Tsaro na Kasa, ƙungiya mai ƙiyayya da Yammacin Turai da anti-Semitic da aka kafa a watan Fabrairun 1942 don tallafawa ƙoƙarin yaƙin Japan. A shekara ta 1945 lokacin da Allies suka ci gaba da kai wa Philippines hari, Matsui ya sanar a rediyo cewa Japan ba za ta taɓa janyewa daga Philippines ba "ko da Tokyo za ta zama toka". Ba da daɗewa ba bayan haka ya kuma bayyana shirye-shiryensa na yin magana a taron lacca a ranar 20 ga Agusta yana adawa da duk wani mika wuya. Duk da haka, a ranar 15 ga Agusta, 1945, a gidansa a Atami Matsui ya ji Sarki Hirohito ya sanar cewa Japan ta
sun mika wuya ba tare da wani sharadi ba ga Allies.