Need help with 3BP boss.

First, I recommend you to get all the Ushi CE, another Golden CE & a support with a Golden CE LB.

You will have a hard time dealing 6M (but still possible) with your team so you should focus on dealing at least 1.5M and surviving the 15 turns. You have the tools for that : Mash, Hercales (if you have his bond CE) & Cu, all with Golden CE if available in this order in the backtline.

For the frontline, Jalter (Ushi CE LB or not), Shiki (Ushi CE as a backup damage dealer or Golden CE) & Support Waver (Golden, LB if possible). Shiki will generate stars for Jalter and try to maximise Arts chain to spam NPs or a Crticial Brave Chain from Jalter.

Use The Battle Suit as a Mystic Code and Guts don't work with Ibaraki's NP so keep that in mind.

I can tell you with confidence that you cannot kill the boss or stall 15 turns with your setup consistently because I have the exact same servants + a max out hans. I succeed maybe once out of every 3-4 tries.

You need at least 2 MLB support +100% CEs. And MLB Ushi on jalter.

Too RNG dependent. If iburaki decides to crit you or use a single damage buster card on any important servant. You lose on the spot.

The only real way to do this raid with your set up is to stall. That means start leveling all the CUs and saint george etc.

You won't kill the boss. Maybe out of 3-4 runs. I finish without dying once with like 4-5m DP every 3-4 failed attempts. If jalter eats a crit. You just lose because you not only do not have enough damage but you don't have enough stall servants.

The only times I have depleted all 6m hp is when my jalter NP buster chained with waver buff and a level 10 ephemerial dream doing like 3m+ damage.

The only real way to kill the boss reliably and consistently is to have 2 wavers. Only real way to stall is to have like a level 90 Cu. He doesn't have enough hp at level 70 even with 8/10/8 skills. 1 crit will end him.

And avoid killing hands until the turn of their NP. Hands do less damage than iburaki.