Natasha Romanová

Natasha is a human from Ultraman Orb that was Gai's best friend, but he failed to save her in the battle against Maga Zetton.

History
Natasha is a human being from 108 years ago that befriended Gai Kurenai, having been best friends with him and clearly Gai cared about her a lot, and she is commonly seen in flashbacks with Gai, however, the friendship between Ultra and Human didn't last as when Orb defended her in the battle against Maga-Zetton,the latter knocked her unconcious, and Orb, who became angered, unleashed all of his might on the Kind Demon Beast of Light, but this caused a massive explosion that killed her, leaving Orb traumatized and depressed from this.

Trivia

 * Gai's interaction with Naomi among other things point to Natasha being Naomi's former self.