Kimagure de Kodomo Hirotta Onna Boss to Sekaiichi ii Otoko ni Naranakya Ikenai Otokonoko no Hanashi

It was love at first sight. In his mid-teens and having to shoulder the debt left by his father, on his knees he swears that he'll become the best man she's ever met. Be this or surrendering his life, she'll collect what's owed one way or another.