the entire night, the period of time throughout the night

nighttime, the night, the period of time during the night

late at night, the middle of the night / midnight

忍び: doing something secretly, travelling incognito; theft; ninjutsu, ninja

discreet, hiding one's identity

不忍: Shinobazu, a Japanese family name

篠笛: Japanese transverse bamboo flute

俊信: a male given name / 利信: a male given name

忍び入る: sneak into

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend