Somebody explain what happened in this film *spoilers*
OK, the presumption was that surrealist master Kaizawa Soichi died recently and has left his mansion and effects to his long-estranged daughter. Nami just happens to be a video game designer creating one based on childhood nightmares (which later prove to be flashbacks), so her boss/ex-beau Kohei decides to use the actual mansion as their game setting. While the pair are at the remote estate, they meet who they think is the disfigured caretaker, who hands them a ring of keys to open the various locks within.
Once inside Nami & Kohei (one of her Dad's fans) find cobwebs everywhere, uncatalogued portrait paintings on the walls, one room with many antique dolls, and in one relatively clean bedroom a music box with a pic of twin infants with the names "Nami" and "Naomi" written on the backof the pic. Nami is shocked because she has no memory of a twin sibling. [I must point out that the syllable "mi" is represented by the kanji for feminine beauty "Bi" in both names so as NOT to make the twist ending over obvious]
In the next phase, they uncover SECRET spaces behind hidden doors and panels using keys found in the house that were not on the keyring. The first secret door in her Dad's study leads to a secret studio within which is an unfinished painting ("Woman with Eyes of Flame"), a scrapbook detailing the disappearance of Naomi at age 6, and the mummified corpse of a child (dressed and bewigged as an antique doll). The freaked couple attempt to flee, but a falling tree splats Kohei's car.
Returning inside Nami showers while Kohei wanders about. He goes back to the music box and finds that someone has stuck pins in the eyes of the pictured twins. Someone tries to abduct Nami from the shower, but Kohei arrives in time to drive him off. At the home office, Shinichi and Toko begin using data transmitted back to them from Kohei's laptop to help the pair at the mansion with useful info. Toko uses the pics from Kohei's vid-cam to map the mansion and deduces there should be a room under the main stairwell. Within this room they are shocked to find a housewide video-monitoring system and a PC with hi-speed access (whose live feed and hard drive files are then sent to the home office compter). Shinichi notices a noose is now dangling in front of the kitchen camera.
Nami and Kohei investigate and see what they assume is the caretaker hanged from a ceiling beam. Approaching the body they instead spot a loose floorboard, which proves to be an unsecured secret panel beneath which are 6 more mummified children in doll drag! Unnerved Nami and Kohei return to the monitor room without discovering that the "caretaker" was merely a dummy. At the office Shinichi uncovers movie files from the mansion computer of Kaizawa in studio with his model -- a chained NAOMI! Before viewing the incriminating files, Kohei sends Nami upstairs, where she does her own snooping using Kohei's laptop. Meanwhile, Toko discovers that the only children reported missing in the area were seven BOYS over the last 12 years! [This is the twist giveaway before the reveal]
Using the laptop to more closely examine the uncatalogued portraits, Nami deduces that they are all of the same model showing her aging from childhood. Kohei in the computer room turns to see Nami standing in front of the monitor board, while at the same time being shown in the bedroom using the laptop withing the monitor board. Realizing he's facing a crossbow-armed Naomi, Kohei tries to flee but is shot through the thigh and falls from the second floor getting knocked cold. Nami comes out of the bedroom and follows Naomi up a pulldown staircase (the one from her flashback nightmares) and into Kaizawa's real studio in the attic where Naomi has brought "Woman with Eyes of Flame". Naomi pulls off the long wig to reveal HE is actually her twin BROTHER and has lured her to the mansion in order for her to complete the canvas for him. He points out that Nami's childhood drawings adorn the walls because Kaizawa missed her. He then sets fire to the attic and stabs out his own eyes. Nami finishes the painting as the mansion blazes into an inferno.
NOW, THE DOUBLE TWIST: The preceding reel was only a scenario within Nami's video game. Nami and her friends are really back at the head office testing it. She then runs an alternate scenario in which Kohei rescues her from the fire, only to be grabbed by her father's reanimated corpse reaching out of the ground for her. Shinichi and Toko are impressed, but in a voice-over Nami exclaims that that was not the ending she produced! Triple Twist?