This was related to the fact that Nobuhiro's brother Nobutake TSUGARU had sheltered his associate page Shigenari ISHIDA as well as Tatsuhime in Tsugaru after the Battle of Sekigahara.
信枚の兄・津軽信建が小姓仲間であった石田重成と辰姫を関ヶ原の戦いの後に津軽に匿っていた縁からである。