In Disgaea 5 there is an Evility called "Gender Bender" that you can equip to any character.
Disgaea 5 and 6 has Girl Laharl as a separate DLC character. There is an option to pass a bill to turn him back into a girl again.
Happens to Laharl in Disgaea Dimension 2, but only for one Episode.
Apparently their choices in weaponry also affect the outcome as well, which gets weird when you figure that the angels in-game are all female. Lamington states that angels have no set gender to begin with, instead taking in traits from the environment and their own emotions having an effect.
A stranger example comes from the Disgaea Novels.
If that's not enough, you can choose to turn him into a penguin instead.
Disgaea allows you to transmigrate any non-story character into another class, with the option of changing gender in the process.
The Flavor Text suggests this ring was used to hide Gwyndolyn's gender. The ring changes your character's animations to use the opposite gender's, but not your voice.
Dark Souls III has a weirder version in the form of Reversal Ring.
For most players, they won't notice anything has happened until they take damage for the first time and their character's voice has suddenly shifted to those of the opposite gender, given that armour pieces rarely have alternate male/female differences, and various animations, while different, are fairly subtle in their differences.
Dark Souls II has an open coffin in Things Betwixt that a daring player can climb into, if they're willing to tackle the two rather powerful ogres positioned nearby.
For example, Miyako turns into Hatsune Miku when Blissed.
It just gets weirder in this fanvid made in M.U.G.E.N.
look at him when Demitri is draining his lifeforce. His Midnight Bliss form has become very popular as a result, ironically turning every gamer's worst nightmare into every hentai artist's dream. Capcom: SVC Chaos, Goenitz is one of the playable characters.