『背中』

案の定発熱していて床に伏した幼馴染のお世話をする瑞鶴。汗を拭こうと背中を見ると、思ったより広くなっていることに気づく

As expected, it's a fever, so Zuikaku tells her childhood friend to sit on the floor so she can take care of him. When seeing his back as she wipes off his sweat, she realizes how much broader his shoulders have become.