Welcome back Idun~
Bravely Default - My HPs, the defaults do nothing!
This post will be about Rusalka. For those who don't remember, Rusalka runs a five-turn cycle. On turn 4 (9, 14, etc.) she will use Seep, becoming untargettable for the rest of the round as well as the subsequent one. On turn 5 (10, 15, etc.) she will use Dark Flow, which does about 1000 water physical damage to everyone. It ignores default. It also summons three clones of her with similar offensive stats and 2700 HP (which is not a negligible amount), though they can't use Seep/Dark Flow themselves. Otherwise all turns are spent on a basic physical, Aqua Regia (water physical which lowers Def), and Charm, which is the worst. No, Dark Flow is the worst. Second worst then.
This fight would generally get my nod for being the hardest boss in the game normally, and is brutal with my team, which lacks MT or good healing. Fortunately it does have Spell Fencer, which provides two crucial weapons. One is Thundara spellblade (the only L3 spellblade I've bought so far), which hits weakness here and is obviously great. The other is a trick I haven't used yet, the Spell Fencer Level 6 passive, Magic Armour. It causes the caster to half elemental damage of the spellblade element he or she has just activated, for four turns. Blizzard Spellblade thus turns into a 4-turn "half Dark Flow" buff which is extremely important.
I toy around with different strategies. I even try leaving the clones alive, since I'm all ST, but this invariably fails, I spend way too many turns healing and charm sooner or later destroys me, that is if Dark Flow against a not-fully-healed party doesn't first. So yeah, clone-killing is the only viable option. And... there's a problem here, I actually only have one PC who can reliably two-shot the clones. Agnes the L3 ranger can... but only sometimes. Ringabel the L6 ranger is the only one who does it reliably. Anyone without a bow doesn't have enough Atk. So it's extremely difficult to reliably wipe the clones in one round, and I tend to hardly end up doing any real damage to Rusalka herself, and charm can really mess things up. Even if it doesn't, I estimate that I'll need about 80 Hi-Potions with this strategy, something I can't afford.
Okay I lied, this post isn't all about Rusalka, because I eventually decide I can't beat Rusalka when I get to her. So I go grind get some JP by doing an obviously meaningful sidequest with important rewards for my team.
Mephilia - Normally a pretty good boss herself, but I'm three dungeons after where she is "supposed" to be fought so she isn't too bad now. I default for three turns, tanking the summon she unleashes on turn 3, then blitz turn 4. On turn 5, I realise that if I repeat the blitz, I'll win, but if she gets a turn before I can kill her she'll summon two allies, who will likely wreck my BP -3 team. So I play it a bit safer, heal up, default turn 6 with everyone to tank the summon and attacks, hope confuse doesn't do things which are too bad (it doesn't), and win from there.
So yeah, after this I have my two reliable clone 2HKOers. But after some experimentation, I realise that, thanks to Aquatic Slayer which Ringabel picked up, Ringabel + Aeolian Bow + Thundara Spellblade + Aquatic Slayer + Hermes Sandals (for the extra hit)... can actually OHKO the clones. Not always, but experimentation yields "more often than not". This is pretty great! Thus, the winning strategy:
Agnes, L5 Ranger with Spellblade and an Ice Charm (there's only one, sadly)
Edea, L8 Monk - pure healer with a shield
Ringabel, L7 Ranger with Spellblade and Hermes Sandals (again, there's only one)
Tiz, L7 Spell Fencer - pure healer with a shield mk2
Ringabel notably has as much defence as he can possibly get, which includes a Cross Shield for defence when he isn't attacking, and the rather pricy Mirage Vest from Florem. This is so Dark Flow doesn't OHKO him, since I don't want to waste his turns switching between ice and thunder spellblade. (When I first tried the fight before any setup monkeying, he was OHKOed. It was bad.) The healers have the highest-def accessory since nothing else helps. Everyone has HP+10%, Agnes has PAtk+10%, everyone else has Magic Armour (not that RIngabel ends up using it).
Anyway, I default for the first three turns. If someone is charmed, the fastest person shield-punches them out of it. On turn 4, when Seep is used, I have up to eight turns to work with (if nobody was charmed). These are spent on setting up spellblades (ice for the healers, thunder for the attackers), healing any chippy damage taken (Ringabel at full HP is a must), and, if the spare turns exist, trying for one attack with each of the rangers. Turn 5, switch back to shields and default for all that it does nothing.
On turn 6, Ringabel is the only PC who reliably goes before the enemies, due to Hermes Sandals. (A fact which messed up many previous runs.) This is where potentially OHKOing is so helpful. RIngabel aims one Aquatic Slayer at each opponent, hopefully killing the clones. Now, the enemies can potentially get turns. If someone is killed, that's bad, since BP is such a premium in this fight. The faster healer (Edea) uses BP to try to minimise the chance of this. If charm lands at this point on someone yet to act, that's also terrible, especially if it's Agnes since she has a real weapon and has braved to the max (this tends to mean an instant loss if it happens). Fortunately, Agnes and Edea at least on average go before most/all of the enemies due to better speed. Agnes aims one Targeting at each of the four enemies, which will finish off any Ringabel didn't kill, and any he did kill just get redirected onto the boss. Finally, Tiz does some healing of his own.
If all went according to plan, then we're back at turn 2, essentially, in the old cycle. The attackers have one less BP than last time, but their spellblades are already in place, so a similar strategy can kick in. This time the "extra healing" that takes place before Dark Flow will likely need Hi-Potions (whereas Potions often sufficed the first time).
On the winning run, after the second big blitz (and a few other minor hits) on turn 11, I realise that I've done enough damage (~27k of the ~40k needed) to potentially blitz out a win, so I switch everyone to offence (the healers equip real weapons and use Thundara Spellblade Hidden Dragons), dumping everyone to -4 BP on turn 13, except Ringabel, who reliably acts before Seep on turn 14. I kill on turn 13 anyway thanks to a crit or two. Hooray! On the winning run I'm able to keep everyone alive which is hugely helpful, and not 100% reliable, but nothing too bad ever happens (Ringabel is never charmed, nobody is charmed before they act on turn 6/11), so while I have modestly good luck this strategy is certainly repeatable. I was Level 29 when I got to Rusalka (and fought Mephilia), Level 30 when I won. Nine resets total.
Onto Chapter 3!