|“||Don't underestimate me. The two of us put together are actually a full-fledged adult!||„|
After the final events of Lotus Land Story, the heroine stumbles upon another strange world which Gengetsu's younger sister Mugetsu claims to be her world. Once Mugetsu is defeated Gengetsu comes to her aid, even while admitting she doesn't even know why the heroine is there. Little is known about either her or her sister and they appear to have no importance to the story.
Gengetsu has yellow eyes, medium-length yellow hair, has a red bow in her hair, and wears a pink and white dress and a red vest. She has white wings.
- Mugetsu (Younger twin sister)
- "Gengetsu" means "illusory moon" when the kanji are read separately; read together they mean "paraselene" or "moondog", which is a type of optical illusion.
- The title of Lotus Land Story's Extra Stage is "Puckish Angel", and the white wings that she has look like angel's wings... For a demon, she's quite angelic...
- The final events of Lotus Land Story occurred in a "Dream World." The place Mugetsu and Gengetsu reside in appears to be yet another dream world.
- Her boss theme contains a short part of Yuuka's Stage 5 boss theme, Sleeping Terror. Also, the main melody is quite similar to Sakuya's Stage 5 boss theme, Luna Dial. However, it is quite common for Touhou songs to have allusions to other songs.
- Gengetsu is able to fire a laser similar in appearance to the Master Spark.
- She is believed to be one of the hardest bosses in the entire series. Even ZUN has referred to her as "the most terrible, most fearful boss" in the music comments. ZUN's remarks were made before Mystic Square and the Windows games, but considering how bullets were harder to see in the PC-98 and other player-unfriendly quirks, this claim may remain uncontested.
- The optional timeout phase of her last attack pattern has been given the nickname "Gengetsu Rape Time" by western players because of its extremely fast and hard to dodge bullets.
- Gengetsu is the only character to be fought in a Touhou game as a 2nd Extra Stage boss directly after another Extra boss; in Lotus Land Story's case, the 1st boss is her sister Mugetsu. Reimu Hakurei has also been fought as a 2nd Extra boss, but this was in the 1st game of the Seihou Project, Shuusou Gyoku. She is fought after Marisa Kirisame.
- In some instances, Gengetsu (along with her sister Mugetsu) have been shown with Nue Houjuu from Undefined Fantastic Object due to the Extra Stage midboss in Lotus Land Story.
- For some reasons, fans depicted Gengetsu with an insane and bloody personality. Many fans compare her with Flandre Scarlet for this fact, and in some Fanworks are seen together, sometimes also with Mugetsu.