Elf to Hitotsu Yanenoshita

Uesugi Kage is a second-year high school girl. When she's suddenly notified that her apartment building is going to get torn down, she is at a loss for what to do. So she asks to meet with her landlord to see if they might be able to offer a solution.

Elf and JK, living together with a 1,000-year age difference.

(Source: Mystery Bonita, translated)