Buy upgrade pills in shop upgrade each attribute to max in the 6 on the bottom then using 20 breakthrough pills upgrade the top one && keep repeating

42k from base susa to gold

Activate the ramen collection for an extra 60 stamina every day

Give him shinra tensei active && yin yang release for passive. Both available in the shop. ^ignore that

The shikakus behest needed to train him in dungeon 25-1 along with 5 daily konan frag packages but has somewhat of a bad drop rate btw

Since you have kaguya, have you tried having her in your formation instead of haku? Her skill has a chance to nullify all effects of their attacks for a couple rounds

If you go to the giftpack tab keep scrolling && there's a page or two you can use recharge coupons on. Mainly toads ninja dog parks or seal stones

Any tips on beating mifune