The Y Investigation is a side quest available in the mid-game. Several assassination attempts are made specifically on Eric(a)'s life, usually with a hate-filled note signed as "Y". Eventually enough clues are left behind for the player to begin trying to track them back to the source.
Preceding Incidents
Multiple incidents occur prior to being able to actually begin the investigation.
- After returning from the trip to Earth, provided the player has at least had the first dinner with Isabelle in the cafeteria, a present will be found in the dorm hall addressed to Eric(a). Inside the present is a bomb which will immediately explode, causing some damage.
- Following the explosion of the first bomb, near the entrances of some mid-game dungeons (Harpy Peak, Ice Sanctuary, or Misty Woods), an ice trap will go off, once.
- At the Watanabe Inn on the third day an Assassin is sent to kill Eric(a).
- Returning from the Inn, the next day in the hallway a mail fairy is present, delivering a letter and package for Eric(a), which is yet another bomb. This time, the bomb was too shoddily made and fails to detonate. After removing the explosives, the mail fairy leaves behind the rest of the bomb to Eric(a), as enough evidence to begin investigating.
The Investigation
With the bomb parts and letter in hand, Eric(a) can now begin investigating the sender. More than one route can be taken to get to the answer.
Bomb Route
Initial Clues
- Julie: As Eric(a)'s friendly purveyor of illicit goods, Julie is the first point of contact about the bomb in hopes she either knows something or knows somebody else who would know more. She recommends Scorch as somebody that likes playing around with machines.
- Scorch: As it turns out the Gentle Magical Girl often hanging around the well is in fact named Scorch. Looking at the remains of the bomb she recognizes the cheap clock it uses as something a blue-feathered harpy tried to sell to her before.
- Tilia: Meeting Tilia in her tree (assuming previous events involving her proceeded to this point) and showing her the remains of the bomb has her finding a tiny seed inside it. She is able to determine that the seed comes from a type of flower that grows in a peak full of harpies, more specifically "a flower that grows about 2.64 meters above of where a young siren set up a shop."
Key Evidence
- Liria: At Harpy Peak is Liria, a blue-feathered Harpy shopkeeper Eric(a) may have ran into before. She mentions selling the clock to a cowled girl with either a sword or hammer, mentioning they came out of the nearby ruins. Liria will then show Eric(a) the secret passage to get there, placing the player directly in front of it..
- Hidden Ruins: Searching the Hidden Ruins map for any remaining clues, the only thing of note in the room to be found is a page of torn notes.
- Torn Notes: The text of the Torn Diary Pages found in the ruins comes from a diary, with these pages bemoaning another failed spell in the writer's attempts to fix their "underdeveloped bust."
Letter Route
- Sophie: Speaking with Sophie in the Administration Building at night, provided she has already been interacted with to whatever results, will have Eric(a) mention that somebody tried to blow them up. Sophie is quite shocked at the murder attempt, and examines the letter written in blood. She determines it is from a human female that has drunk a lot of Gob-Gob brand lemonade.
- Giselle: As the cafeteria lady, Giselle is the one to ask about foodstuffs. Giselle names Krislka as the only girl capable of drinking Gob-Gob Lemonade more than once.
Coming to a Close
- Krislka: Both roads lead to Krislka, the Green-Haired Magical Girl that has been around the camp in the background. She often laments about the size of her breasts, and is the only one that can stomach Gob-Gob brand food. Talking to her will have Eric(a) either automatically show her the Torn Diary Pages, which she immediately recognize as hers, or bring up the bomb and Gob-Gob lemonade blood letter. After Eric(a) explains the situation Krislka denies sending the bomb, but mentions having left her belongings in a secret passage only to later find it gone. She then shows Eric(a) the secret passageway entrance.
Conclusion
Entering the secret passage, a few steps in will have a voice call out to Eric(a), commenting that they are finally here and it is time for them to talk. An opening will appear on the wall in the passage, within which there is a small hidden room where Y is waiting.
Acknowledging they sent the bomb Y then reveals their identity, casting off their cloak. As it turns out, the person named "Y", who hates Eric(a) to the point of trying to kill them, first showing themselves after the events of the trip to Earth is in fact... Yvette!
Yvette is a character that had not even been named before, lampshaded by Eric(a) in the dialogue. She had however long since been a background character, the Blue-Haired Magical Girl that constantly fangirled over Isabelle. This now proceeds into the boss battle against Yvette.
Results
- Winning against Yvette will provide the Serpentine Core.
- Eric(a) is assured by Isabelle that Yvette will be punished. She can later be found as a statue in Marianne's junk room.
- Access will be retained to the secret passage and Yvette's secret room.
- Yvette's diary is available in the room and can be read. It details the beginnings of her obsession with Isabelle as well as her descent into madness and hatred against Eric(a).
- The secret room contains another secret passage leading into the Administration Building, useful for after the passage from the well is sealed if Eric(a) does not have the Maid Transformation.
- Losing against Yvette will lead to the Death Knight Game Over.