Sasuke can taste their blood, an addicting metallic tang that fills him in the darkness where he can't really see them (where he can't be tempted to stop before it's too late).
Naruto murmurs something in his almost unconscious state, trying to reach him, trying to reach Sakura. Sasuke can hear her tears, her body giving up slowly; he knows Sakura doesn't have any chakra left to heal them.
"Sa-- Sa… Sasuke-k-kun," Sakura whispers.
Sasuke can't say anything, his body covered with their blood. Sasuke can't resist his urge when he starts licking it from his hands, from his arms; he even leans towards them when Sasuke can barely hear their breathing to taste more. Naruto tries to move his body but he can't, he only moves his lips against Sasuke's before a mute name leaves his mouth. Sakura grabs Sasuke arm when their lips meets, without any strength left and her tears are almost a plea which Sasuke ignores. Sasuke doesn't respond to them; he already did before.
He waits.
Soon it will be over, Sasuke thinks.
He is killing them at his own whim. He is killing them before anyone else can.
Because they're ninja; and dying is not a promise, but a destiny.