Miyu Sakai (坂井三悠 Sakai Miyu ) is the third and only remaining child of Kantarō and Chigusa Sakai and the younger sister of Yūji Sakai. She was introduced in the last episode of the anime and in the short story Future from volume SIII.
Miyu is an infant girl who has short dark-colored hair.
Not much is known about Miyu's personality since she is an infant.
She was born after the last fight in Misaki City between Shana and Yūji, so they never had the chance to see her. Ogata occasionally visited the Sakai residence to take care of Miyu. While enjoying the scenery of the Sakura Festival, Kantarō reveals his daughter's name and the meaning behind it to Yūji's former classmates at Misaki Municipal High School. She was named Miyu because of the distant sound (はるか, which can also be written as 悠) that he and Chigusa heard during the last battle (Shana versus Yūji and Margery Daw versus Sydonay). This was most likely when Yūji commanded the residents of Misaki to watch and remember the scene.
Miyu appears in the final chapter of Future, titled Sakura Festival. At the night of the said festival, Margery Daw presents a ring she called "St. Edward's Ring", which in reality is one of the ten rings of the Treasure Tool called Chorde - and the only one left on Earth. Shana used this Treasure Tool to combat Yūji in the last battle. Margery says that if one takes hold of the ring and prays, the hopes and prayers would reach the other rings. She passes on the ring to Eita Tanaka and Ogata, who pass it back to Margery and Keisaku Satō, who then pass it on to Ike, to Yukari Hirai, and finally to Kazumi Yoshida. Miyu, upon watching the whole scene, cries and seems like she wants to hold it. So the ring is given to the Sakai couple, and ultimately to Miyu. They pray and as the chapter closes, they say their prayers and their blessing becomes a wind that would cross between worlds.
- Her name may imply 'superior beauty', 'superior feeling' or 'the third child who will live long'.