Fatal Frame: Mask of the Lunar Eclipse is a 2008 survival horror video game developed by Tecmo, Nintendo SPD and Grasshopper Manufacture and published by Nintendo for the Wii. It is the fourth installment in the Fatal Frame series and the first on a Nintendo console. Initially released only in Japan, a remaster for eighth and ninth generation consoles and Windows published by Koei Tecmo was released worldwide in 2023. The story focuses on three characters investigating the abandoned and haunted Rogetsu Island: Ruka Minazuki and Misaki Asou, two girls who were involved in a secret ritual and suffered amnesia as a result, and Choshiro Kirishima, the detective who rescued them. The gameplay, as with previous entries in the series, revolves around the main character exploring environments and tackling hostile ghosts using the Camera Obscura.

The idea for Mask of the Lunar Eclipse came to series co-creator Keisuke Kikuchi when he first saw the Wii hardware. Kikuchi and series co-creator Makoto Shibata returned as respective producer and director, while Grasshopper Manufacture's Goichi Suda acted as co-director, co-writer and designer. The addition of further developers to the project enabled the team to reconsider the standard formula, although it proved to be a chaotic experience. Tsuki Amano returned to create the game's ending themes. The Wii release became the best-selling title in the series up to that point, and was praised by Japanese and Western critics for its atmosphere and mechanics while being mixed on its controls. The remaster also saw strong sales, but was met with mixed reviews due to the age of some gameplay elements while praising the scenario and art design.

Fatal Frame: Mask of the Lunar Eclipse is a survival horror video game that has players taking control of four different characters navigating a variety of different environments, including traditional Japanese houses and a Meiji-era sanatorium-turned-hotel, while facing hostile ghosts through photography using the series' recurring Camera Obscura. In the original version, third-person navigation and first-person control of in-game weapons such as the Camera Obscura are controlled using the Wii Remote and Nuchuck. The 2023 remaster reworks these for each console's controls. During exploration, the characters are regularly attacked by hostile spirits, who take away the characters' health through touch.

The two central characters can fight off and defeat spirits using the Camera Obscura. Shots taken by the Camera Obscura deal varying amounts of damage based on how close the ghost is, the angle of the shot, and the film used. These factors are taken together to determine how many points the player is awarded for a shot. The most damaging type of shot is the "Fatal Frame", which is achieved if a shot is taken when the ghost is attacking. Points are used as the in-game currency, which can be used at save points to purchase items such as medicine and other items. Blue gems scattered around the environment can be used to upgrade the Camera Obscura, with some upgrades speeding reload time or enabling shots to deal more damage. Types of film range from an unlimited low-quality film that deals little damage to rarer and more powerful film types.

In addition to the Camera Obscura, the third character can use a flashlight to explore their surroundings, and one character has access to a special Spirit Flashlight, which uses moonlight to pacify spirits. Should a ghost attack, gestures with the Wii Remote can shake them off. The "New Game+" mode unlocks additional costumes and further items and upgrades, many of them dependent on how much the player has scored during the initial playthrough. On higher difficulties, the number of items available is reduced.

In the 1970's, ten years prior to the start of the game, suspected serial killer Yō Haibara kidnapped five girls from their rooms in a sanatorium on Rogetsu, an island south of Honshu. The girls were rescued from a cavern beneath the sanatorium by detective Choshiro Kirishima, who had been pursuing Haibara, but they had all lost their memories. Two years later, a catastrophe strikes Rogetsu Island which kills off the inhabitants. Eight years later, in the present, two of the rescued girls have died in mysterious circumstances and two of the survivors, Misaki Asou and Madoka Tsukimori, return to discover the truth about their pasts. Despite being warned by her mother not to return to the island, fellow survivor Ruka Minazuki goes there to find Misaki and Madoka. Shortly before Ruka's arrival, Madoka is killed by hostile spirits. Choshiro also returns to the island at the request of Ruka's mother Sayaka, intending to both find Ruka and continue his pursuit of Haibara.

During their explorations, the characters learn that the island once used a ritual to send spirits to the afterlife during a decennial lunar eclipse, which countered a supernatural disease called Moonlight Syndrome, which affects memories and identity. An earlier failed ritual which triggered a mass outbreak of Moonlight Syndrome caused many elements to be forbidden, including the ritual dancer's mask dubbed the Mask of the Lunar Eclipse, and the melody "Tsukimori" that survived through Ruka's family. By 1970, a kagura was used in its place and became a tourist attraction, although Moonlight Syndrome was a continuing problem. Ruka and Misaki were among the infected treated at the sanatorium with Haibara's spiritually sensitive sister Sakuya. It was decided to conduct a new ritual, with Ruka's father Soya Yomotsuki crafting a new Mask of the Lunar Eclipse. Sakuya was the lead dancer wearing the mask, with Ruka, Misaki, Madoka and the two other girls taking part.

Due to lacking "Tsukimori", the ritual was a failure. Sakuya reached the final stage of the disease and fell into a coma while shattering the mask, the other girls collapsed and suffered amnesia, and the kagura dancers all died. Two years after the girls were rescued and left the island, Sakuya woke up and infected the whole island, killing everyone including Yomotsuki. Misaki―a descendent of the Camera Obscura's creator―was drawn back to Rogetsu by the spirit of a doll given to her by Sakuya. Choshiro is also revealed to have died that day, killing the fleeing Haibara after being fatally stabbed.