The following is a translation of the Project Justice tier list found over at Justice Gakuen Gakuen, specifically focusing on the sections explaining each of the tiers. This should be useful for understanding why certain characters are placed in certain tiers, as each section briefly explains why a character has found themselves in their respective tier. Bear in mind that I'm not a professional translator (or even completely fluent in Japanese), so there might be a couple of sentences I've screwed up. Hopefully I've gotten the message across, though.
S: Roy, Kyoko, Hyo, Hideo
A: Hayato, Kurow, Kyosuke, Roberto, Yurika
B: Vatsu, Burning Batsu, Zaki, Batsu, Edge
C: Shoma, Hinata, Boman, Momo, Natsu, Tiffany, Akira = Powered Akira
D: Nagare, Daigo, Wild Daigo, Demon Hyo, Gan, Ran
E: Chairperson
S Tier
Roy and Kyoko are incredibly strong rushdown characters, thanks to their incredible jabs, strong pressure tools and high damage.
Hyo excels at preventing the opponent from pressuring him, thanks to {{#motion:f}}{{#motion:lp}} being an incredibly strong Tardy Counter, and his {{#motion:qcb}}{{#motion:p}} having a large sidestep on its startup, both of which also start combos which then lead into his own pressure.
Hideo is arguably the game's best keepaway character, being exceptionally good at keeping the opponent at bay with a mixture of air fireballs and divekicks.
Hyo might instill a couple of bad habits, but in general all of these characters are very easy to use, and exceptionally strong.
A Tier
While Kurow is very strong, Hayato has really managed to solidify his position in the tier list.
Hayato's gameplan is both strong and incredibly simple and consistent, which really makes the character shine.
Kurow, on the other hand, has potential to make more of an impact if some dedicated players really worked to optimise him.
Kyosuke and Roberto are basically in a fixed position on the tier list at this point. It's possible that there may not be anything else to discover with these characters.
Yurika is extremely good at defensive play and walling people out, but much like Kyosuke and Roberto, there don't seem to be any groundbreaking discoveries with this character on the horizon.
Because the S tier characters have such strong overall gameplans, the characters in the A tier seem slightly more difficult to use by comparison.
B Tier
The ever-changing Batsu Series. This time, Vatsu finds his way to the top thanks to his strong offensive options, Burning Batsu comes in second thanks to the strong close-range game afforded to him by his confirms from crouch jab, which leaves normal Batsu third. However, while these characters all play fairly differently, there isn't much of a difference in strength between them.
Although Zaki finds herself in the B tier, she's got the tools to compete with the characters in the S and A tiers fairly consistently. However, she doesn't exactly destroy all of the characters below her, so B tier seemed to be the most appropriate spot.
Edge is a character who relies a lot on counters and tricky resets in his air combos, but those resets seemed to work less and less over time, which affected his overall strength.
C Tier
This tier is mostly for characters whose strengths are generally overshadowed by their weaknesses.
In the end, we can't really say with certainty that Momo is a particularly strong character. She suffers a lot from her poor range, lack of good approach options, and low damage in spite of her combos, which mostly leaves her relying on combos into Party Up. After all, if it takes Momo three combos to take the round, then that puts her behind all the other characters known for their high damage.
By comparison, Hinata and Natsu have steadily risen on the list, thanks to adding 0.5 judgements to the matchup chart. Powered Akira has returned to the C tier for similar reasons.
TL Note: This is referring to the addition of 0.5 decimal judgements on matchup calculations, which improved the positions of these characters as far as the numbers are concerned.
D Tier
Ran and Demon Hyo have moved around in this tier a lot more than Daigo has.
To be honest, Ran is basically a worse Hinata or Akira, and she's heavily reliant on resets.
As for Demon Hyo, his weaknesses more or less speak for themselves if you try to use him. His neta stuff is pretty interesting, though.
E Tier
Despite her ability to more reliably confirm mini launchers from light attacks, and other ways the character could have grown, Chairperson was basically doomed to be here from the start. Because she was intentionally made bad, she kind of just gets screwed by everyone else, at least as far as damage is concerned. The new strategies found for the character didn't make up for the character's overall low effectiveness, but at least the five minutes spent messing around with her was interesting.