A few notes about Mystery’s tails (The Future spoilers)
So just to start out, we see Mystery had 6 tails during Ghost.
Then during most of The Future, he has 7 tails. He has 7 from the moment he changes in the beginning and bites his arm. He may have had 7 during the small shot we saw of his kitsune form in Freaking Out but it was hard to tell with how the shots were ¯\_(ツ)_/¯ I think there may have concept art around that time with 7 tails? Maybe the 7th appeared with Lewis’s death, since the 6 tails shown in Ghost was a flashback of the cave?
Then Vivi gets hurt by Shiromori. We see this blue energy burst out of Mystery’s heart and an 8th tail appear.
Then he gets hurt and Vivi smacks Shiromori’s heart out of the park. Mystery looks horrified as she crumbles and now white energy bursts from his heart. Now we see the 9th tail appear, and Mystery faints.
Mystery then is possessed by the spirit of the cave, likely due to the emotional stress making him let his guard down. Also supported by Arthur’s conflicted emotions being implied to make him a target for possession. A weak heart likely = easy possession.
(The colors I find interesting since they seem to pertain to certain people (or even events). Shiromori was white (fitting since Shiromori means “white forest”). Vivi was blue. Yellow could’ve been due to the incident with Arthur’s arm and maybe pink for Lewis’s death?? But there’s obviously a lot more going on here and the seeming connection to his tails is a tad confusing. Could it just be a case of his powers going out of control due to the distress? He’s been concealing himself for sometime so??? It’s hard to speculate on that point with the little it we’ve seen so far. )
Note: Mystery does seem to have 9 tails in Hellbent during the quick flashbacks with Shiromori.
Some notes about Kitsune from various folklore:
The more tails they have the more old, wise, and powerful they are.
They can shapeshift, though typically into humans.
Some tales say they have a hard time hiding their tails while shape shifting.
They gain tails as they age. They get their 2nd tail at around 100 years old, and the 9th at 1,000 years old.
9-tailed kitsune can be white or golden colored. They’re called Tenko at this stage and considered celestial beings.
Kitsune associated with Inari are also white. They are called Zenko.
Kitsune are true to their word, and may sometime attach themself to a household to repay a debt.
They will use their powers to help their companion as long as the human treats them with respect.
They are generally mischievous and cunning, and will play tricks on the arrogant, prideful, and greedy.
They can create illusions or visions.
Do with all this what you will. Add to it, correct it, whatever. I’m just trying to get down all my observations before forgetting and returning to the void.