I would play it as a battle only the axe wielder and the spell could participate in.
*** D&D Speak Follows :) ***
A spell would get stats based on the level of the spell - HP and AC, with both improving by level.
0-2nd level spells would count as an object, so you just need time to chop through them unopposed.
3-5th Have 'physical' attacks to defend themselves, causing invisible damage to the axe-wielder.
6-9th Have special attacks and likely to preemptively 'attack' the axe wielder if they come close.
Probably the easiest would be to take a monster of the appropriate level, removing their movement abilities and re-skinning them as the spell. Monsters with minimal special defenses would probably make the most sense.
Other characters might be able to help if they have spells that can interact with spells. Or if you allow multiple weapons in your world with this ability.
I think this is a more interesting approach to removing spells then just the Dispel Magic spell.
To be honest, I like this a fair bit. I would've given it a 4 except that the bits at the end invite a lot of questions from me and leave me quite unsatisfied. But I get Cult of Done, just a pity for this particular idea. Go to Comment
The item just fell from the sky one day. Everyone assumes it was from the gods, but a close examination by a person of knowledge will reveal this is clearly a work of complex handicraft from some unknown being. Perhaps a passing UFO tossed it out with the trash. Go to Comment