Bows should be two-handed, as they require both hands to use properly. You’re already not allowed to twoweapon with them, but it shouldn’t really be possible to wear a shield and fire a bow at the same time either, except maybe a small shield. Possibly classify them as hand-and-a-half weapons, in variants that have those, or just disallow firing with a bow while wearing a shield.

One-and-a-half-handed weapons that are capable of being used either one-handed or two-handed. They default to two-handed if the player is not wearing a shield or twoweaponing. They have better damage stats than pure one-handed weapons, but the damage is reduced if it is used one-handed.

The description for the katana says it can be used as a two-handed sword. Maybe twoweaponing could be adapted for this, i.e. use both hands on the weapon for an extra damage bonus based on strength, at the expense of being able to use a shield.