Cyber Shadow

The video below shows how to defeat Biohunter using only your sword, thus unlocking the Blade's Plenty achievement/trophy.

Remember to avoid buying the weapon power up at the save station before this boss. You must enter this battle only with your basic sword.

Do not use magic or special attacks. Only direct blade hits.

If you like me get the secondary weapon before the boss, just backtrack a few stages and receive a few hits. This way you'll loose it. Then go for the boss fight just being careful at the station/checkpoint just letting yourself healing but not getting the weapon. You can walk without stopping on it and get the heal recovery but not the sec weapon.