Speed

He pressed his forehead protector onto his head, and steeled himself.
Farewell for now.
Itachi’s body moved faster than his thoughts. Before he knew it, his little
brother was in his field of view. At that moment, he understood for the first
time that he was looking back. His desire to burn the image of his brother
into his mind had moved his body.
But that was another thing he could not be permitted.
A mistake ...
Because Itachi could feel the hot tears streaming down his cheeks. He
quickly turned away from his brother, and resumed his jump. The aura of
Sasuke collapsing behind him, he leaped into the moonlit night, not bothering
to wipe away his tears.

Book of Dark Night Chapter 6