Happened to me today - not sure what causes it as it has only happened once and I have done lots of runs

I've changed to just levelling Kika's weapon and using the rune of punishment with hero, the potch spared can be used on defensive equipment.

Switched out Sigurd for Viki for an extra kindness rain, and gave an alert rune to Jeane so that her spells improve at the battle mid point.

This method gives success nearly every time, but still requires a levelling session at the final boss (to level 57) and a return to ship to get equipment. The return to the ship is a massive time loss as cannot use escape talismans or the glowing hand mirror.

I've been practicing this game getting ready for a new game run. Having a few problems with the final boss.

Does anyone have any tips?

I am using Hero, Kika, Sigurd and Jeane. Just standard runes and basic equipment so as to save time in the run - and weapons are strengthened to 9 (except Jeane who is 1) so as to limit potch grinding.

If I level on the final stairs to 57 - I can beat the boss sometimes, but it's not super reliable unless I return to the ship to spend the potch gained on jizo clocks.

Any advice welcome, thanks