Given Clue: She has yet to appear in the Walfas Adventures storyline. Mai and Yuki have NEVER appeared in Walfas Adventures at the time of the clues' writing
Hidden Clue: To find this clue, you need to look at images 73.png, oh, and Badendpart3.png ^^;. If you downloaded Badendpart3.png, you would notice a faint link, which is the URL for Mobile Fish Steganography. Trying to use it on the image, you would get a insignificant text which I refuse to tell. Trying it on 73.png, on the other hand, would get you this:
Cheers, mate! The culprit is often associated with a certain fairy.
That certain fairy being Cirno. Both Mai and Cirno's powers are associated with Ice.
Given Hint: The culprit has appeared only in the PC-98 games. Mai is the Stage 4 boss for Mystic Square, which is Touhou 05, which is STILL the PC-98 Touhou game, the very last, for that matter
Hidden Hint: You should be looking at 76.png. And as for what tool to find the clue....it ends with a 'Stego' :3 I used OpenStego, but anything with a 'Stego' works. Using it on image 76.png gives you a text file with the words:
The culprit is actually working in a team!
Yuki and Mai both attack you until you defeat one of them.
Given Hint: She is (probably) the ONLY character who has words in her letimotif's name that describe her character. Mai's letimotif's name is Treacherous Maiden ~ Judas Kiss, and technically in the game, if you defeat Yuki before her, she will shrug and say that Yuki was holding her back
Hidden Hint: Today's hidden hint is brought to you by image 717.png :3. Steganography is used again (see clue 1), but be aware that not only do you have to FIND this clue, you have to figure out what the hell it means! Again, using Mobilefish. Using it on image 717.png will give you a text file with only the words:
DECEIVING THE HEARTS OF PEOPLE!!!.....yeah, figure out what the hell that means.
'Ma' can mean deceive, and 'Kai' can mean 'the hearts of people', so yeah.
Given Clue: The culprit may or may not be evil in canon, which practically rules out Utsuho. Because of Mai betraying Yuki, most people think she's evil. The reason why the clue says that it rules out Utsuho is because it was CONFIRMED she was evil (for a short while), whereas Mai can only be seen as a jerk.
Hidden Clue: Brought to you by image 720.png! You'll have to use Stego to find it....and figure out what the hell it means! Again, using Stego, and using it on image 720.png will give you a picture of Stinkoman. The reason for this being that he is the Trope namer for 'You Gotta have Blue Hair' and Mai has blue hair.
Given Hint: Marisa is....rash in decisions. Yes, this means the person she confronts may or may not be the culprit. Pretty darn obvious.
Hidden Hint: All this clue gives you is a picture of Yumemi and a link to Stegmuffin. People who are rash will quickly assume that Yumemi is the culprit, but using Stegmuffin on the image will give you an image of Yuki and Mai (which I cannot find for some reason).
So yeah, not many people actually BOTHERED to look for the clue, and pretty much no one could find out who it was. God knows whether or not I'll do it again, but if you guys want another challenge of this, let me know ;)