Heya!
I'll explain EVERYTHING about Hamedo:
First, what triggers it is PHYSICAL ATTACK. Since monster uses SPECIAL ATTACKS, Hamedo doesn`t work.
SPECIAL ATTACKS are rather different from PHYSICAL ATTACKS or MAGIC ATTACKS.They can be counered, but never hamedoed even if your brave was 100000000. Choco Ball or Choco Meteor can be countered by Counter Magic, But not Hamedoed. The same fro choco attack: It can be countered but not hamedoed.
If you`re equipped with a Bow, Crossbow or Gun (including magic ones) you may ONLY counterattack/hamedo the ranged attacks. It will not work for near ones. Spears or Papyrus will counter/hamedo the same as normal range. Harps will only counter/hamedo 3 panels away of attacker (so, it will only counter bow/gun attacks, but since only a sucker archer would attack from 3 panels of range, don`t use hamedo/counter on bards... anyway, their PA sucks).
So... only use HAMEDO when you`re in Story Battles and you`re facing humans.