As always

The Unfalling Fortress is a tough spot. To block the row-one attacks, you need to solidify your front-line defense or reinforce your formation with support magic. Not rushing and taking it one step at a time is the warrior's path.

The row-attacking sentry you have to fight... Are you talking about the Corrosion Eye (the one with tentacles coming out of its eyes)? Surprisingly, what the AI above said is quite accurate. That beam from its eyes, despite appearances, is a physical attack, so if everyone targets can guard, you can exploit an opening. That's one way to attack it. * It's easily crushed by its double-action, but if you have Blade's Retribution, you can strike during its opening before its next action. For the same reason, if you use Iaido as a Samurai, you can dodge and attack. Bring someone like Camille and use an incense to block its skill. * The Healer's spell skills are quite effective, so I recommend it. There's no benefit to prolonging the fight, so it's better to use skills and finish it off quickly. As for consumables, you can only recover the Nourishing Potion from the starting 8th floor by doing Kasuho daily and bring as much as you can carry. Honestly, if you can defeat this guy, you've basically won the first week's gatekeeper.