小太郎(こたろう)は松王丸(まつおうまる)の息子(むすこ)であり、菅丞相(かんしょうじょう)への忠義(ちゅうぎ)のために我が子(わがこ)を身代わりに(みがわりに)した

In truth, Kotaro, who became the substitute, was Matsuomaru's biological son. Despite being on Shihei's side, Matsuomaru had not forgotten his loyalty to Kan Shojo, who had bestowed favors upon him in the past. To save Kanshusai, he had enrolled his own child in the temple school beforehand, arranging for him to be the substitute. Matsuomaru and his wife wept as they spoke of their child's tragic death, singing of the pain of sacrificing parental love for loyalty. It is a heavy tragedy unique to Japanese classical theater.