The Master of Ragnarok & Blesser of Einherjar: Mizuki Shimoya

Yuuto's childhood friend whom he has a crush on. She is able to call Yuuto using the phone he still possesses while he is close to the divine mirror that summoned him to Yggdrasil. When Yuuto is returned to the 21st century, while she is ecstatic, it doesn't take long for Mitsuki to realize Yuuto wants to go back, so she resolved to go with him. After managing to convince Yuuto that she won't back down on her resolution, she accepts Yuuto's marriage proposal.