During Chapter 3 the story will make you visit Reiji. He will speak about a great invention which is the Battle bot simulator and can be accessed any time during free movement at the Underground Hangar.

There are 9 different battles and they have to be beaten with each Flower Division member as your partner for a total of 45 battles.

Every time you finish one story combat section, 5 new battles will be added to the simulator. This battles are nothing more than a simulation of the story combat sections, same enemies and same bosses. Actually, any story battle you finish with an S rank will already be recorded as beaten and you don't have to play it again, so aim for an S rank during the story too.

Beat all 45 battles with an S rank and the trophy will unlock. Check  ​A Great Fight​​​ for details about how to achieve S rank.