This is an early review for Guilty and only a limited amount of people managed to get their hands on her, so it's hard to do proper testing.
Skill 1 - Mind If I Borrow This?
■ Activates after landing 6 normal attack(s). Affects self.
Mind If I Borrow This?: Duplicate 8.81% ATK of ally with the highest ATK, stacks up to 5 time(s) and lasts for 10 sec.
The best skill in Guilty's arsenal that makes her a top-tier boss killer. While it takes her some time to stack the buff up (and also if she gets stunned it can drop off), it makes her DPS so good, she beats even dedicated Burst III attackers on Bosses.
And to make the skill even better - the stronger the character from who she copies the ATK gets, the stronger Guilty gets. So she doesn't only scale off her own levels and gear, but also off your main carry.
Skill 2 - Time to play
■ Activates after landing 12 normal attack(s). Affects all Wind type allies.
Increases stack count of buffs by 1.
ATK ▲ 4.13% for 10 sec.
Similar to Rupee, Guilty can help allies with increasing their stacks of buffs, but for Wind characters instead. Sadly, there are not many Wind characters that are meta at the moment, so it's hard to make use of the skill.
Still, the skill also affects Guilty herself, so she can stack her S1 buff faster and also gets a small ATK buff which further increases her damage output.
Burst Skill - Gotcha
■ Affects 1 enemy unit(s) with the highest DEF.
Deals 284.32% of ATK as damage.
■ Affects the same target(s) when Mind If I Borrow This? is fully stacked.
DEF ▼ 20.25% for 5 sec.
Deals 277.71% of ATK as additional damage.
Guilty's Burst skill is a simple single target nuke, but the multiplier is a bit on the lower side compared to other single-target Burst skills. Still, even this adds up to her damage potential. The DEF debuff is a nice bonus, but in the current damage formula, you don't really feel it that much.
Guilty has a unique mechanic that allows her to duplicate part of the ATK of the highest ATK ally, which massively increases her damage output, especially when you pair her with a character that already has a lot of ATK. Still, the ATK stacking ability has a ramp-up period, which means Guilty's DPS will be smaller at the start of the battle and she unlocks her full potential after around 25 seconds. This makes Guilty more viable on bosses as the fights last longer.
As for Guilty's Burst skill - it deals decent damage and also lowers the DEF of the enemy which even more pushes her toward the dedicated boss killer role. And with the Burst having just 20 seconds, you can use her as your solo Burst II character too!
Overall, among the Burst II characters Guilty dethroned Rupee when it comes to the damage output she brings, but to achieve that you have to pair her with a high ATK character. Still, compared to Rupee, who can also buff the ATK of all allies with her Burst, Guilty can only affect Wind allies with her S2 (and the ATK buff value is much lower).
Story - S across the board in all stages. While she's a more single target-focused unit, her damage output in Near stages is actually really good,
Bosses - SSS in both solo Bosses and Bosses with adds. Guilty's damage output is simply crazy and she can out-damage Scarlet even on solo Bosses.
PVP - A. Sadly it's hard to make use of her in the Shotgun meta team as her Burst generation is on the lower side and it takes her some time to ramp up her damage.
Since getting Guilty is impossible for F2P now, there are not many videos out here showing off her performance, but here's Tim's mini-review of her and also skyjlv's video showcasing some gameplay with her.
Keep in mind that's just base Guilty damage output vs Scarlet and other characters that have multiple dupes.
Sin and Quency
Most of the whales have chosen Guilty as their character of choice in the Liberation mode, so it will take some time to release the reviews for the 2 other characters available there.