Nodoka: Sadly, she sucks. She is the best accuracy buffer in the game but there is no content that requires that yet, accuracy is important in PvP but you want to bring characters that have naturally high Acc anyway, not to mention it's all RNG so her AoE EX that buffs accuracy could hit just your tank which would be a complete waste.
Swimsuit Tsurugi: Decent. A high damage pseudo-tank like regular Tsurugi. She loses her ability to sustain herself but gears her kit more towards pure damage, with her EX buffing her damage output. She often punches way above her weight and is similar to Serika in that way. If you're missing some blues she's a great auto-attacker for a welfare. (Auto-attackers are characters who need very little micro, they have an EX that substantially buffs themselves, and their basic skill does a lot of damage to one enemy)
Swimsuit Izumi: Ok. Her kit is not impressive but her EX can stun up to 5 enemies which is very useful in situations where you want to avoid an enemy's special attack, that's of course if they can be crowd controlled. (Crowd control is any skill that shows up as purple in the status bar, they restrict a character's action in some way, for example a stun makes them unable to act, while for example Kayoko's fear makes them unable to act and they run away).
Tomoe: Very niche. She's only useful if you're specifically running her with Mutsuki to make sure Mutsuki's minefield basic skill doesn't whiff like it usually does but instead does MASSIVE damage, since Tomoe's EX lowers attack range forcing Mutsuki to go to the front in that situation, while also boosting her movement speed, crit % and crit damage.
Fubuki: Good. She's another decent auto-attacker, this time yellow. Her EX takes a loooong time to go into effect since she literally has to eat her donut until it goes online but it's a substantial buff. Her basic skill inflicts a lot of damage and stun, which is why she can be pretty useful, especially for the Hod raid boss who needs to be crowd controlled.
Michiru: Decent. Can stack buffs on herself to do a lot of single target damage with her EX. Her problem is that she's a shotgunner and she really doesn't have enough HP, defense or self-sustainment to be a pseudo-tank like Reisa or Tsurugi.
Swimsuit Ayane: Very good. Virtually a 5th striker auto-attacker at the cost of one special. Unlike most other specials that arrive in a vehicle, her EX that makes her appear in an attack chopper is cheap as fuck while also doing tons of damage. Her only downside is that this is all she has - damage. But DAMN does she do a lot of it, and since her EX has low cost, if you combine her with a low cost yellow team you can basically keep her on the field at all times.
Swimsuit Shizuko: Probably the best welfare student though that's after you build her up a bit, your priority should be getting tracksuit Hasumi. Anyway, she is a very versatile character that can do many things, in most other games a jack-of-all-trades kind of character sucks but in Blue Archive they're often the best ones because their flexibility helps a TON in teambuilding (other examples of that would be Kokona and new year's Fuuka) and swimsuit Shizuko is no exception, imo the best welfare for now. She buffs everyone's attack (have to 3* her for that tho), she buffs your highest crit student with MORE crit damage as her basic skill and her EX repositions and shields but as said earlier she's a special that offers no damage by herself so you need to build her up before she becomes useful, it's well worth it tho.
Cheerleader Hibiki: Insane damage, insanely slow attack speed, her insane damage is from TWO MINUTES of damage over time. That makes her very niche as you need to find situations where someone's gonna sit there for 2 minutes and eat up all that damage.
Track Hasumi: Like regular Hasumi but blue and with a better overall kit. Due to circumstances already explained, you can already 5* and 3* her weapon, that makes her a great crutch character for new accounts because you get a very strong blue damage single target unit, and her rolling EX cost allows for a lot of flexibility. Has the same pitfall as regular Hasumi - big single target damage is all she has so she's a bit of a glass cannon or maybe a better comparison is to say she's as squishy as her boobs.
Maid Yuzu: Good. Especially if you're missing red AoE, maid Yuzu does that job very well, also buffs the entire team's attack once you get her to 3*.
