19 kimi is Ikenushi.
20 The sentence ends with kofuru. The next sentence ends with nayamase (31), of which the logical subject is, hototogisu, understood.
243
Hototogisu wo yomeru uta.
Haru sugite 1
natsu ki-mukaheba
ashihikino
yama yobi-doyome
sayo naka ni 5
naku hototogisu