TLDR: chud with no sense of strategy defeats galdera after 30 hours of trial and error fighting with no guides and a shit ton of luck
No one I know acutally plays Octopath (even though I've been talking a lot about it these past weeks to them) so I'm celebrating here lol
so I've only played a couple of turn-based, strategy games, that being Persona and OT. The Persona series as a whole is famously not that hard, with a few execptions. In OT, I'm usually overleveled to the point where I don't need that much strategy, or really just a simple strategy.
Back in OT1, I did finish Galdera, but I cheesed it via Winnehild's Cry and even that took me a while to figure out. So when I got into OT2, I said I wouldn't cheese this boss, or even look up guides (I did look at a few optimization builds but ultimately did not use any of them)
This took me 2 weeks, and I added around 25-30 hours just for trying Galdera (that's how much of a chud I am at strategy)
Omniscient Eye team: Osvald (Dancer), Paritio (Cleric), Ochette (Merchant), and Temenos (Scholar)
I used Osvald as the main damage dealer, and built his support skills all around just doing as much damage as possible. Partitio and Ochette were for breaking and support ie Beastly Howl to lower defense. Temenos was on healing, support for Osvald, and rarely secondary damage.
Galdera: Hikari (Armsmaster), Throne (Merchant), Agnea (Cleric), Castti (Merchant)
You can tell I way really relying on merchant's Hired Help for breaking at this point lmao
I used Castti as a BP slave and Hikari as a main damage dealer. Agnea was on Cleric in order to heal and use Aelferic's Blessing for Hikari and Castti. When first breaking him, Hikari used Lionheart's Axe on him full boost for a 70K+ damage attack. Throne had previously used Armour Corrosive and Hikari had boosted physical attack. Each Hired Help's Veterans did around 40K damage. Hikari was able to do Lionheart's Axe 3 time in total, twice with full boost. Throne and Castti both did Hired Help once, with 40K damage.
I was so sure I was going to die, but apparently not!
I acutally spent hours making this strategy (basically texting friends different strategies and finding out they didn't work in practice) and I had quite a few strategies in mind haha. In the end it took a lot of luck and praying...