Does anyone know about the 301 key? （I've completed the story.）

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Does anyone know about the 301 key?
The ending left the mystery unsolved.

[Kid Named Finger]

I believe 301 and 307 cant be opened. They have holes near the doors to see through and get codes for safes

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The ones that are set not to open are 303 and 305.
301 requires a key, so I think it's somewhere.

When I cleared it, I had a cat frame and one dissolving liquid left over, and nothing happened when I placed a flower pot (a setting error?), so I think it might be one of those...

[redchaostry]

Did you use the solvent (dissolving liquid) on the back of the bathroom door on the 2nd floor to get a coin?

Im stuck on the Annex Server room door lock.

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That was the remaining solvent.
Thanks for the info.

I don't remember the door lock, but I think it was one where you matched the security code with a poster on the floor...

[MiKowaii]

About 303.. how do you peek to see the code? To be, the card holding the code is hanging low, with only "right 10" visible.
This is pure curosity, I've already brutre forced the lock

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Update 1204
There was a "Thank you for your hard work" letter and coins in front of the flowerpot from the beginning, but this seems to be a setting mistake. It seems that the reward was just given from the beginning.
The battery added in the update was already the key code for a cabinet that was opened with another hint.

The only remaining mysteries seem to be the 301 key and the cat picture.

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The mystery of the cat picture has been solved.
It seems that due to a setting mistake, it was the key to a locker that was open from the start.

The only mystery remaining is the location of key 301...
I have a feeling this is also a configuration error.

[hyeorn]

I have no idea if you already figured out, but I'm just putting comment here to let others know about 301 key. 301 Key is located at EPS Room on 1st floor. You can get bolt cutter after final boss and then go to EPS room not the Nell's room. Then, go to 3rd floor using elevator.