For those who dont know you acquire the Battler's blade by building up enough tribute (tribute unlocks swords, enough tribute you unlock the battler's blade).
I've actually done the first level with the Battler's but without A+, you can just run through quick to get the Battler's blade for the first level but i recommend trying for A+ also..
Dont forget your brutal difficulty to get that achievement too!
All video credit goes to Sewerrat0..