Toyoshige had interactions with Shungaku MATSUDAIRA (the lord of Fukui Domain), Munenari DATE (the lord of Uwajima Domain) and Nariakira SHIMAZU (the lord of Satsuma Domain), and these four lords including Toyoshige were called Bakumatsu no shikenko (the four remarkable daimyos of the end of the Edo period).
豊信は福井藩主・松平春嶽、宇和島藩主・伊達宗城、薩摩藩主・島津斉彬とも交流を持ち幕末の四賢侯と称された。