Eunis was a neighbor of Linda Tran.
Eunis lived in Neighbor, Michigan, as the neighbor and family friend of the Tran family.
After Kevin was reunited with the Winchesters they went to Linda's house to make sure she was safe. They quietly took out two demons guarding the house outside and then they knocked at the door. After Kevin reunited with his mother Sam and Dean entered the house to see if there were more demons.
The demon possessing Eunis tried to flee the scene after getting spotted by Sam but Sam performed a reverse exorcism and then was stabbed by Dean with the Demon-Killing Knife, killing it. Linda was horrified by what she saw but Sam and Dean later explained Eunis was possessed by a demon.