Location: Auguste Isles, "Baruha Beach", Chapter 9, "Crashing Waves, Rising Beats" This is a battle between only your main character and not just one, but three members of the Fundoshi Trio (Soriz, Eugen, and Jin [story found in the 'Gird Your Fundoshis' Grand Blues Channel quest]). They are also the legendary Baruha Beach fishing festival bearers (founders of some fishing festival [and its chief initiation]). Basically, you will have to tough it out with three burly bros of rippling beach near-nakedness. It's that side of nature so off to it.
First off, you are faced against the King Pin, who is actually much easier to deal with than the trio. All you have to do is keep on healing (and maybe some debuffs). Eventually, the King Pin will cave in and let you grapple against the trio. However, you can notice the peculiarand debuffs. It's kind of a hint entailing what the trio will do to you. Obviously, you are not going to make many hits and charge up within time. It's going to be a slow ride.
Now, the second episode and last stage is a endurance test, none of that hit lingo. I must remind you that your main character will be pitted against three foes alone. An assessment on the data table shows what each foe can do. Soriz got thatdebuff, so you will have to fight him first anyways. Eugen specializes in charges with debuff and buff. Jin is basically a (big enough) damage dealer. All their special techniques will activate on maximum charge diamonds. Their charge diamond cap is quite short as well.
You will be peppered by a number of things. A shield protecting a charger and damager. Since you are overwhelmed, it is best to outlast against each foe. Weapon skills and summon auras are constant passives to help hold out against the trio. In endurance, healing is essential for most of the battle, so provide enough sources in either skill, weapon, or summon. Speaking of health, it's best to tagas your support summon should you fall. Other than health, you may want to look into mitigating damage. and debuffs and and buffs can help. Just make sure that you happened to be quite successful in either debuffing or buffing. I would advise you to invest into the as she can defend, heal, and charge at the same turn. Offense-wise, if you are a charger, expect to forget about (consistent) charge attacks because Eugen will try to disable you. Rather, try to increase attack rate to deal more damage and replace the role of charge attack. Last, but not least, remember to stack up the elemental weapons for more damage. Make sure their weapon skills work out for you. The same goes for your wielded main hand weapon.
During the battle, you can see different quantities in each foe's charge diamond cap. If you attack the most (Eugen) to defuse a charge situation, you can count on the other two to start pummeling away with their own charge attack. It's best to remove the least first as charge attacks tend to be not so easy to withstand. Oh yeah, Jin does have a HP trigger that increases his charge diamond cap as well as his charge damage. That's when you start multi-attack and charging. There's critical damage, but I doubt it's significant in impact.
That being said, you should be able to take down the trio in a one-by-one fashion (without losing a). You can try out an all-foe attack method, but it's still a endurance test to me. Anyways, enjoy that Drum Master class.