Are you casting Aeroga on your party members as well? --- Gamefaqs has taught us that academic fields like literature don't exist because of teenagers that say "well that's just your opinion and I disagree."
Aeroga On-> Stop -> Ragnarok -> Aerial combos until the Ragnarok blasts end -> Ragnarok again -> Aerial combo until Stop wears off --- "Ganondorf needs to forget everything he's ever learned about tennis and train to become a competent sword fighter." - RATTfink138
I dunno if their attacks actually decrease your score or if they just don't count. But what I do know is that the number of MP is what's the deciding factor here. The more MP you have, the longer Stop lasts. So, for 100 hits, bring in as much MP as you can: so equip Diamond Dust (+3), 3 of any combination of Atlas Armlets/Royal Crown/Shiva Belt/Cosmic Arts (+6), and be at least level 60 (if you chose Sword), or 72 (if you chose Staff or Shield), as well as have Aerora/ga & Ragnarok. iirc, the maximum amount of MP you can have then is 17 (Sword & Shield) or 19 (Staff), which means Stop would last for 34 or 38 seconds.
After that, all I can really say is good luck to ya. Lock-on to the head, apply Aero, Stop it, then unleash Ragnarok. The 3rd one's rays likely will just barely hit it in time. --- Things I learned from Earthbound: Toothbrushes blind people, mushrooms are evil, and trees explode when they die.