A/N: Please check out my other Fili and Kili fanfiction called Me and You Against the World. Please send in prompts for this! Enjoy.
Fili doesn't know why this happens. He doesn't know how it happens either. Well yes he does. Ever since Kili was old enough to leave the crib, that's when it started.
Fili was worried that because Kili was so small he let him sleep in his bed with him. He fell asleep on one side of the queen bed with Kili on the other. When Fili woke up in the middle of the night his little brother was curled up next to Fili his arms wrapped around Fili's left arm in a tight grip. It then happened the next night and the night after that and finally it became a routine for Fili. Go to bed with Fili on one side and Kili on the other. Then sometime that night Fili would wake up and Kili would be curled up at his side. Fili would tuck the blankets around his brother better and then fall back asleep.
Then one day, Thorin bought them their own beds. Fili thought that their night time routine would end. Fili went to bed that night totally fine. However later that night he was woken up my a poking at his side.
"Fee. Feeeee." Kili whimpers.
"Hm?"
"I can't sleep." Kili whimpers and tugs on Fili's arm.
Fili sighs and moves over. "Climb in." he gruffs.
Kili climbs in and snuggles up to Fili almost immediately. Fili tucks him in like always and then falls back asleep.
The next morning Fili pushed the two feather mattresses together to make a huge bed.
"Now you won't need to wake me at night." Fili smilied.
Kili's grin lit up so bright Fili teased Kili for months that it blinded him.
Years later on their quest for Erebor the first night they slept in the wild Fili didn't expect him to wake later that night.
But behold late that night Fili awoke to see his brother sleeping next to him, one arm across Fili's chest and the other wrapped tightly around Fili's arm. Fili laughed to himself. Kili never changed.