Mission Tree: http://www.gamefaqs.com/console/xbox360/file/944262/58302
note: to obtain the KIKU blade weapon which does stupid amounts of damage, complete mission 24. Defeat Red Rum & Starka on normal.
To obtain the Moonlight blade which is more of a long slash as opposed to the kiku basically just being a single tiny punch that packs nuclear damage. To obtain it you must defeat the 5th ranked ORCA arena opponent, Shinkai. To see how to easily win all the tournaments refer to my solution here:
Mission 12: Defeat the Spirit of Motherwill
Normal: AF Motherwill (2 large clusters of 3 cannons, missile pods)
This can be an extremely intimidating mission if you're not prepared for it. Equip an OGOTO and a KIKU or MOONLIGHT blade along with the 051ANAM shoulder unit (whee... flares). Overboost straight for Motherwill and fly up to the towers on the left and right.
Blade them quickly. By now, your radar will show missiles coming at you, so fire your flares and quickly take out the missile pods located on the rotating wing sections. You can identify these by the massive barrages of missiles they keep shooting. :P Try to keep airborne as the NORMALs located on Motherwill's wings can cause unnecessary damage to you. Use your radar to track missile proximity and the flares to throw them off. It's easy to miss an objective target as well but use your radar to track them all down. This mission can easily be S-Ranked in under 3 minutes with a little practice. If you are having ammo problems, go with dual OGOTOs.
S-rank strategy credit to CastorCat