Catherine

Catherine is the only unit in the game that can provide teamwide invincibility for those precious few seconds. Just because of how many stages you can cheese with this invincibility, she is an extremely easy SSS tier for campaign stages, no matter where you are at the game.

There have been times when you can run a level 120 Catherine with a team of 200/180s and she still serves her purpose as long as her S2 kicks in. If you have tried to RNG clear a stage long enough, you will know even milliseconds make a difference as to whether your tank lives 1 hp more so that your healers can heal it back up to at least 30% hp. No other healers can provide the same amount of raw sustain as she does, and you can expect to use her in almost every single Elite stage (in multiples of 5, with Adrienne/Ayame/both). Her S2 is the bread and butter skill we know her for, while S1 and S3 further make your team that much healthier. M1 gives a respectable amount of heal in a pretty large radius, and can sometimes cover your entire team in certain scenarios such as an enemy Clarie jumping into your team and everyone lumps together. Her ult is also rarely used due to opportunity cost, as most of the time you want to kill the enemy DPS with either AOE or single target burst with your ults.

Single Bosses

Currently the boss stages are heavily focused on dealing as much damage as possible in a short time frame, and Catherine’s heals are simply not needed at the moment until more bosses with bigger damage come along.

PVP

Catherine is also an essential unit especially for future defense stall comps, since you currently lose a match if you cannot kill all 5 of the enemy’s team. Her S2 and M1 give respectable amounts of healing, contested only by Jiho’s single target burst heal since your units are likely focus-firing a single unit.