I Promise You.

" Unweathered and untethered light
I promise you, I promise you
Take my strength
I honor you with everything
Take my strength
I promise you and I will see it through
You lay dreaming
The endless light you shine on me
All I needed "

I can imagine this as the last picture taken of them at Trost District, the morning before they left for the Battle of Shiganshina, for the final operation to retake Wall Maria.

Based on Hajime Isayama's Attack on Titan characters, Commander Erwin Smith and Captain Levi Ackerman.