Yes i can; go to the phantom realm by Honoji temple, & have Ako wear the red vest, keep killing demons until you can enhance everything to it's MAX level, you can't use your weapons in the final battle, but the Onimusha sword gathers power from your others, so if they're all at lv. 2 it'll be lv.6, If they're at MAx level, the Onimusha sword will be lv.9 or MAX...I'm not sure about this, but you might also get bonuses from the Bishamon sword.
Secondly, in the phantom realm, you can always go back & get the meds on mid floor. Enemies drop lots of herbs & if you haven't died much, you should have talismans. Make sure if you have lots of medicinal items.
Finally, stay in ready position most of the time. You will be able to sidestep all of his attacks. Once you do enough damage, he'll drop the Genma Samonji, absorb it & it works like the Onimusha sword.
Hope it helps
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