AI: The Somnium Files Wiki
AI: The Somnium Files Wiki

Day 5: Tuesday -zugAI- (5日目:火曜日 -頭蓋-, 5-Nichi-me: Kayōbi -zugAI-, lit. Day 5: Tuesday -Cranium-) is a chapter featured in AI: THE SOMNIUM FILES.

It is the twelfth chapter featured in the Ota Route. It covers Kaname Date's investigation of Mayumi Matsushita and his discovery of a new victim.

Case File Synopsis[]

The next day, Date began interrogating Mayumi. However, Mayumi's story was determined to be unreliable. Boss gave Date permission to Psync.

But the Psync machine was broken and needed repairs. With the Psync delayed, Date pursued another lead. On Monday, Mayumi took a taxi and followed the Matsushita family car. The driver testified that the car stopped by So Sejima's residence...and found So's corpse, cut to pieces. Who killed So Sejima?! But in any case, it was confirmed that Mayumi must have been present at the cold storage warehouse. With the Psync machine repaired, Date began the Psync...

Story Summary[]

ABIS HQ, Tuesday 10:04 AM[]

Interrogation Room, Tuesday[]

Mayumi's interrogation.

During her interrogation, Mayumi continued to insist that she was responsible for Iris's kidnapping and attempted murder. However, she was unable to explain how the video was streamed, and some of the details she provided conflicted with the facts of the case. Date was not convinced by her motive for killing Iris or the previous victims. However, the evidence still placed her at the scene of the crime, so Boss told Date to Psync with her.

Psync Control Room, Tuesday[]

Pewter having some com-pewter problems.

The Psync Machine was still inoperable after the Psync with Ota, since Date and Ota were not compatible. Boss gave Pewter a six hour deadline to fix the machine and prepare it for Psyncing, while Date left to investigate.

Driving, Tuesday[]

Driving from ABIS to Matsushita Diner.

Aiba and Date concluded that Mayumi must have been lying to protect someone, likely Ota. They discussed the possibility of Ota being the New Cyclops Killer. Date did not believe it to be possible, but Aiba argued that Iris and Ota could have been accomplices: Iris covered her fingerprints and drove the Matsushita family van, Ota removed her eye, and put the polar bear costume on and off during the stream.

Matsushita Diner, Tuesday 11:15 AM[]

Ota crying at the Diner.

Ota was upset with Date for arresting Mayumi. Date explained that she was not under arrest, but he did take her in for questioning. He also brought up the possibility that Iris and Ota staged the whole incident, which Ota denied. Ota talked about how his parents worked to keep his family afloat after the chemical plant explosion forced Matsushita Diner to close. They were able to send Ota to college, but after a year, his father died, and Ota dropped out to focus on his writing career. Mayumi was supportive of his decision, but Ota did not realize she had dementia and had yelled at her when she forgot he dropped out. After Ota's story, Date told Aiba he did not believe Ota could be the killer based on his intuition.

Harbor Warehouse District, Tuesday 12:50 PM[]

Police at the warehouses.

Outside the warehouse, Date reexamined the cars. After discussing how Mayumi could have driven to the warehouse, Aiba searched for cars that had driven through the area at the time of the incident. She found a taxi, and traced the driver's current location to Lemniscate.

Lemniscate Office, Tuesday 1:36 PM[]

The taxi driver at Lemniscate.

Date met Mayumi's taxi driver in the Lemniscate lobby. He recounted that Mayumi had asked him to tail a van, and gave Date a timeline of events. Around 10:00 PM, they drove from Matsushita Diner to the 8-12 parking lot, where Mayumi purchased the Odoroki-man chocolate. After 10:30 PM, the van took off down the highway and into the Sejima residence. Ten minutes later, the van left, then entered the Kabasaki District. Since the area was restricted, the taxi driver refused to enter, but agreed to stake out the entrance. After another 45 minutes, the van left the district and entered the harbor warehouse district, where they lost track of it. There, Mayumi left the vehicle and headed towards the warehouses, which was the last the driver saw of her.

Sejima Residence, Tuesday 2:21 PM[]

So Sejima's dismembered body.

So Sejima and his bodyguards were nowhere to be found. Date entered the mansion to find the smell of blood coming from a large vase. Inside the vase was So's dismembered body, with his left eye missing. Aiba determined the time of death to be approximately 11:00 AM that morning. When Date asked why the mansion was empty, Aiba informed him that So's wife was dead and his son was living abroad. Pewter called Date to inform him that the Psync machine was ready, and Date told Pewter about So's body.

ABIS HQ, Psync Room, Tuesday 3:09 PM[]

Mayumi prepared to be Psynced.

Date returned to ABIS to Psync with Mayumi. Just before the Psync, Pewter informed Date that an investigation into So Sejima's murder had begun.



  • The name zugAI (頭蓋) translates to "Cranium," which is in reference to both Mayumi Matsushita's dementia affecting her mind as well as So Sejima's dismembered head (and other body parts) found inside his vase.

References to Pop Culture and Media[]

  • During the 12:50 PM investigation at the Harbor Warehouse District:
    • If you examine the "Oil Drum," Aiba will say "Hi, I'm drum-aemon!" This is a reference to the manga series Doraemon, which contains the titular robot mascot Doraemon.[1]
    • If you examine the "Container," Date will think to himself, "If I put that corner container in an empty spot, would the bottom line disappear?" This is a reference to the game franchise Tetris, which operates under similar mechanics to clear blocks.[2]
  • During the 1:36 PM investigation segment at the Lemniscate Entertainment Offices, if you examine the "Sofa," Date will say "Sofa King..." before Aiba tells him to stop. This could potentially be a reference to various things[3], but it's most likely a reference to a Saturday Night Live skit involving a pun with the phrase "sofa king," which sounds like "so fucking."[4]


Kaname DateAI-Ball/AibaIris Sagan/A-setOta MatsushitaMizuki OkiuraBossPewterNew Cyclops Killer
Hitomi SaganMayumi MatsushitaRenju OkiuraMamaShoko NadamiSo SejimaMoma KumakuraRohan KumakuraCyclops Serial Killer
#89FalcoBodyguardsTakero MatsushitaManaka IwaiSaito SejimaYakuza AYakuza BNurseReceptionistMermaidTaxi DriverInspector
Chiyoda District: Police Headquarters (Boss's Office; Psync Room; Interrogation Room) • Sunfish Pocket
Koto District: Harbor Warehouse District (Cold Storage Warehouse) • Date Residence
Meguro District: Sagan ResidenceTiefblau
Minato District: Sejima ResidenceKumakura OfficeIkume ShrineLemniscateCentral Hospital
Near Kabasaki District: Bloom ParkOld Chemical PlantMatsushita Diner
Shinjuku District: Golden Yokocho (Marble)
Other: Fuchu City (Fuchu Prison) • Akikawa ValleyOkutama MountainsEitoku High
SINKIN' IN THE BRaiN (Spoiler) • PSYNCIN' IN THE PaiN (Spoiler)
PSYNCIN' IN THE VaiN (Spoiler) • PSYNCIN' IN THE SWaiN (Spoiler)
PSYNCIN' IN THE VILLaiN (Spoiler) • PSYNCIN' IN THE MaiN: 1 (Spoiler)
PSYNCIN' IN THE MaiN: 2 (Spoiler)
Red Route: sigAIsaikAImeikAIsyokubAIrihAI
Yellow Route: syougAIseisAIhiAIsanpAI
Green Route: gumAIjukkAIkikAIjinnAIihAI
Purple Route: keitAIgyoukAIkyuusAIsyuurAIirAIdakkAIkekkAI
Pink Route: kenzAIjutAIkokkAIsousAIhakAIkassAI
Tokyo Metropolitan Police Department (Advanced Brain Investigation Squad) • Ujisaki Family (Kumakura FamilyKumakura Estates) • Secret Society NAIXATLOZForeign Mercenaries
LemniscateSunfish PocketMarbleTiefblauFamiSto8-12Elgorg
Wadjet SystemEvolverLight Synaptic Nerve Connection DeviceDate's CarShovelForgeOdoroki-man ChocolateGeostationary Satellite X00639
Chemical Plant ExplosionOriginal Cyclops Serial KillingsBreak-In at Sagan ResidenceNew Cyclops Serial KillingsIncident at Minato District HighwayDisappearance of Renju OkiuraOperation: Iris Rescue
Full List of Events


  1. Wikipedia page for Doraemon
  2. Wikipedia page for Tetris
  3. Wikipedia page for the disambiguation of Sofa King
  4. Vimeo video of Saturday Night Live skit