Espgaluda (2003): Once upon a time, there was a peaceful kingdom named Shinra, ruled by a line of queens with supernatural powers. The current king, Jakou, decides to conduct a number of experiments to induce this power in his children as well as harness it for military purposes. Two of his children, Ageha and Tateha, are rescued from his grasp and taken into hiding by a man named Hiodoshi. Eventually, Jakou's forces track them down...
Espgaluda DX (2005)
Espgaluda II (2005): It has been three years since the first game, the events of which are known as the "Great Shinra War." The ruling family of another country named Soma decide to salvage Jakou's research and create an organization called the Spirit Society, dedicated to producing more children with psychic powers. One of the products of these experiments, Asagi, flees and joins Ageha and Tateha.
Cyborg — Seseri, after the first stage of the first game.
Dude Looks Like a Lady — If not for the first game and the other two characters as references, you might not realize that Asagi's alternate form is supposed to be a boy, especially thanks to the artwork showing that this male form's shoes have higher heels, and the book is changed to a stuffed bunny head.
Evil Counterpart — Kujaku, the final boss of the first game, is able to do gender-changing Awakening just like the player characters.
Evil Laugh — Madara, the boss with the multi-part tank in Espgaluda II.
Fan Service Pack — In Espgaluda II, Tateha and Ageha have aged a bit, and their clothes for their female forms are noticeably more revealing. Almost literally for Seseri, who was rebuilt to look like she had aged as much as the main characters. (not counting her playable version in Espgaluda II Black Label)
Gender Bender — The core gameplay mechanic for high scoring. The final boss of Espgaluda can do it too. In Espgaluda II, this game mechanic is required for unlocking the fight against True Seseri, and the final boss is a fusion of a boy and a girl.
Guest Fighter — The PS2 port's arrange mode has a character who plays just like J-B 5th, and one who plays just like Irori Mimasaka.
Guide Dang It — The scoring system, especially the Awakening Overdrive mode for Espgaluda II. Then there's the whole gameplay for Espgaluda II Black Label.
Incest Subtext — In the second game, Tsubame and Janome unify into a single being named Kujaku as the final boss. There is a lot of additional subtext between them shown in Asagi's ending. Also present in Ageha's ending, between him and Tateha.
Innocent Flower Girl — Janome, the boss of Espgaluda II stage 3, is strongly linked with flowers. She turns not-so-innocent when she becomes a boss of a Cave game.
Mad Scientist — In the first game, Ageha & Tateha's father is an evil king who experimented on his own children in order to induce Psychic Powers. In the second game, the Spirit Society is doing this on a larger scale on many children.
Magic Pants — An interesting example, in that the characters' clothes magically transform to be appropriate for their current gender, for certain definitions of "appropriate."
“Well Done Son” Guy — Seseri's motivation for wanting to kill Ageha and Tateha, since she was not born from a psychic queen like they were. When she is defeated in the second game, she even says, "Father, I'm sorry..." as she dies.