Ambiguous Gender Identity: It's strongly implied that Hazumu was a trans girl all along without realizing it, and that may have been why she was resurrected in a female body. Prior to being turned into a girl, Hazumu expressed a desire to be Tomari's bride, and she was the only "man" Yasuna could see clearly. She doesn't protest at all about becoming biologically female and seems to be much happier being treated as a girl than she was (presenting) as a boy.
First-Episode Resurrection: Was killed when they were hit by Hitoshi's spaceship. She was brought back to life afterwards, but at the cost of irreversibly switching his gender to female.
Gender Bender: After being killed by a falling UFO, the aliens responsible for the crash revive Hazumu as a girl. However, Hazumu is happy with being a girl, and it's implied that she always wanted to be one.
Happily Married: She and Tomari end up getting married at the end of the OVA.
Girly Girl with a Tomboy Streak: Despite her femininity, she keeps some of her traits from having spent her entire life a boy (such as preferring boyish clothes).
Innocent Fanservice Girl: Justified as she just turned into a girl and is therefore unfamiliar with how she should act, such as using her skirt to cool her legs, and asking Asuta to measure her bust size.