Siel Mail -シエルメール- ① / ルテンの方舟

The story of Ricol, a girl who carries letters in the sky world. Part 1.
Synopsis.
Ricol, a girl who lives in a certain sky world, was asked by the sky god Uranus to deliver letters from the sky world to the ground world, and to send letters from the ground world to the sky world.
One day, Ricol and his cloud buddy Watagumo go to see the mailbox...