Natsuki has been acting strange and seems to have his head in the clouds through everything he does. After being interrogated by Minamo and the others, he reluctantly confesses to them that he kissed Atri in the ocean. 
That's why hearts are difficult.
لهذا القلوب مُعقّدة
Darum sind unsre Herzen
ja auch so kompliziert.
El corazón es muy complicado.
El corazón es muy complicado.
Voilà pourquoi
les sentiments sont complexes.
Ecco perché il cuore è complicato.
É por isso que um coração
é difícil de entender.
Говорят же: чужая душа — потёмки.