Thanks for the tips so far. I messed up with the Monk and gave it a try with “Champion” just to confirm that the Greatshield is perfect replacement for armor.
Besides a Greatshield +13 (defense 0-30) I got a mail armor of entanglement that was cheap to upgrade to +5 (Troll + 1 SoU). Augmented for Evasion since defense is not great anyway, and Entanglement kicks soon enough at +5.
I spared the last SoU to enchant two weapons randomly: Lucky Glaive and Chilling Crossbow, cause the shield was doing great enough at +13. I was hoping for a shocking Glaive or Runic blade but well.
With the Champion’s ability to have the +13 on any secondary weapon it was a relatively easy ride as expected.
This was the kit near the end:
GREATSHIELD IS MY ARMOR With a few more attempts, I can confirm that the Greatshield is a good replacement for armor. Just make sure to have a +10 Greatshield before entering the Demon Halls. There are ways to find one and with a little luck it can be wielded before Tengu!