In order to get the trophy “In The Heart Of Battle”, you must acquire the Hadouken for Mega Man X. It’s the same technique that Ryu and Ken, along with several other Anasutsken practitioners, use during combat.
First, you must acquire all heart tanks, all energy tanks, along with all your weapons you get from the eight Mavericks along with the armor and weapon upgrades you earn from Dr. Light.
Once that’s complete, go to Armored Armadillo’s stage. You will need extra lives, so go on foot, get past the first peacock and keep going until you see a bat that’s not like the others. That particular bat has a high chance of dropping lives. Kill him and grab those lives until you get nine lives.
Next, get to the end of Armored Armadillo’s stage, then die for the next four times. On the fifth time, at the end, jump up to the cliff that’s above the entrance door and you should see a blue capsule. Approach it and Dr.Light will instruct you to enter the capsule for a “special gift”.
Enter the capsule to get the fireball. Once the computer AI takes over and has X perform the Hadouken, the trophy should be unlocked.
It’s important that your health bar MUST BE FULL BEFORE YOU DIE.
Have fun and good luck!