Tsukuyomi is the deification of the moon and the ruler of the night in Shintoism. He was born of Izanagi's right eye as he bathed after his descent to the underworld, thus making him the brother of Amaterasu and Susano-o. Tsukuyomi was the second of the "three noble children" (三貴子, Mihashira-no-Uzu-no-Miko), who was commanded by his father Izanagi to watch over the night sky.
In the Chronicles of Japan, Tsukuyomi and his sister the sun goddess Amaterasu part ways due to their disagreements. This is why the sun and moon appear at different times in the sky.
However, there is so little known about Tsukuyomi that even their sex is unknown. However, in Man'yōshū, Tsukuyomi's name is sometimes rendered as Tsukuyomi Otoko (月讀壮士, "moon-reading man"), implying that they are male. There are many theories behind this mysterious god.
Digital Devil Story 2: Warrior of the Demon City
"Soul of the light of heaven and earth, light of the moon, come here to me, Tsukuyomi!"
Special Forces Agent Narukawa is the reincarnation of Tsukuyomi, and as such, shows a familiarity that he cannot define with Akemi Nakajima, the reincarnation of Izanagi. When Nakajima is tormented by Isma Feed and Set through their torture of Yumiko Shirasagi, Tsukuyomi reawakens within Narukawa. Tsukuyomi quickly dispatches Isma and Typhon with arrows of light and commands that Charles Feed takes Nakajima to safety, identifying Nakajima as an important warrior. Tsukuyomi attempts to hold off Set as they escape, and is killed by the demon.
Shin Megami Tensei IMAGINE
Tsukuyomi was implemented during the 2015 Halloween event and his plug-in was obtainable through it. He possesses a unique feature that boosts his magic abilities and limit break power according to the moon's phase. He can be fused in a triple fusion of inexperienced Yatagarasu, Hecate, and Nyx.
Shin Megami Tensei V
"A god that appears in Japanese legend, believed to be the deification of the moon and the ruler of the night. According to the Kojiki and the Nihon Shoki, he was born from Izanagi, and is younger brother to Amaterasu as well as older brother to Susano-o. Upon fusing with Yuzuru Atsuta and reassimilating his lost knowledge, he thus assumed his original Nahobino form."
—Shin Megami Tensei V lore
After defeating Surt, Ishtar and Arioch, Hayao Koshimizu announces that he will be leaving Bethel and he is in fact, the Amatsu known as Tsukuyomi, and that he will take the throne to return Tokyo to the Japanese Gods. According to him, he was one of the few Amatsu remaining following the defeat of most of Bethel Japan's Amatsu. He also has Yuzuru Atsuta team up with him and act as his Nahobino vessel.
In the Empyrean, if the protagonist chooses to side with Nuwa, he will merging with Yuzuru into a Nahobino, telling the protagonist that even if he was his brother, he will not let him get his way, before fighting the protagonist next to the throne. Should the protagonist decide to destroy the throne (and thus averting the Lucifer encounter), then he will be the final boss. If the protagonist were to side with Ichiro Dazai and Abdiel, he will instead fight Tsukuyomi in where Abdiel should be since he and Yuzuru already killed Dazai and Abdiel, and Nuwa will be fought near the throne. If the protagonist sides with him instead, Abdiel kills him and Yuzuru, Nuwa will confront him near the throne just like the situation before.
Unlike Abdiel and Nuwa, Tsukuyomi cannot be unlocked as a summonable ally.
Persona x Detective Naoto
Tsukuyomi appears as the Persona of Sousei Kurogami. According to Tetsuma Tsuge, Sousei awakened Tsukuyomi not long after Aigis had successfully awakened Palladion, but unlike the latter, Tsukuyomi has no combat ability at all, thus causing Sousei to be classified as a failure. Much like Amatsu Mikaboshi, Tsukuyomi is unable to engage in combat, but makes up for this flaw with a very special ability: Past Reading. This special skill enables Tsukuyomi to hear the thoughts of deceased people up to six months after their deaths. However, if Amatsu Mikaboshi synchronizes with Tsukuyomi, this duration can be extended to three years.
Persona 4 Arena Ultimax
Known as Tsukiyomi, it is the Persona of Sho Minazuki when he surfaces through a Plume of Dusk, and is, befittingly, of the Moon Arcana. During Sho's Instant Kill attack, Tsukiyomi's body is changed by the black substance attacking the opponent, replacing his white lines with red ones similar to Magatsu-Izanagi. His sword also resembles a scythe as it cuts through the opponent, disintegrating them. In the True Ending, Minazuki disappears and Sho inherits Tsukiyomi from the plume.
Its only skills so far from the SMT series are both Life Drain and Spirit Drain, used as command throws. It can also combine both versions into one through a Skill Boost (since both moves share the same motion but end in different buttons for their input/command).
"A Persona of another story. An important god born from the Japanese god Izanagi, he governs over the moon and the night. There are many theories behind this mysterious god."
—Persona 5 compendium
"I am Tsukiyomi. Madness in my right hand, tenacity in my left... Now then, who shall I break apart first?!"
—Tsukiyomi upon being summoned
Tsukiyomi is a DLC Persona belonging to the Moon Arcana, having two versions; one with his original color scheme, and a Picaro version of him. The original version is Lv. 50, whereas the Picaro version is Lv. 55. Occasionally when summoned to attack, the protagonist will shout "Sho-Time!" in reference to the puns made by Sho Minazuki. Furthermore, Tsukiyomi itself references its original users, stating that madness (Sho) is in his right hand, and tenacity (Minazuki) in its left hand.
Shin Megami Tensei: Liberation Dx2
"The moon god from Japanese mythology. Tsukuyomi was said to have been born from the right eye of Izanagi during purification after his escape Yomi no Kuni, the underworld. Tsukuyomi was the second of the "three noble children", who was commanded by his father Izanagi to watch over the night sky. In the Chronicles of Japan, Tsukuyomi and his sister the sun goddess Amaterasu part ways due to their disagreements. This is why the sun and moon appear at different times in the sky."