、。
In the darkness, I desperately stretch my hand out toward her receding figure.
Literal
Darkness [gen-の] inside, I [topic-は] receding back-figure [to-に] desperately hand [obj-を] extend.
A dramatic/reaching-out image. 暗闇 ('darkness') is a compound of 暗い + 闇, both meaning 'dark.' 遠ざかる ('to recede, to move farther away') is an intransitive compound. 後姿 ('back figure, figure seen from behind') is an evocative noun — in Japanese narrative, watching someone's 後姿 is a classic image of longing or farewell. 必死に ('desperately, life-and-deathly') is literally 'with one's death-fate assured,' meaning with all one's effort. 手を伸ばす ('to stretch out one's hand') is the standard phrase. Rich imagery.