This Seeking Tech guide will show you how to get the KO trophy in Astro Bot.
Rescuing Ryu
For the first step, you need to rescue the Ryu bot. He is located in the Retro Rampage 1 stage, which you can access on the upper left corner of the Gorilla Nebula. You will need to ram the controller on the small asteroids and then the big asteroids.
Once you get to Retro Rampage 1, defeat the enemies in this stage to unlock Ryu.
Rescuing Ken
Next, you need to rescue Ken, who is found in the Retro Rampage 2 stage. To get to this level, ram the controller into the meteor on the north side of the Tentacle System.
After getting to Retro Rampage 2, you then need to defeat the enemies to rescue Ken.
KO Trophy
After getting both characters, return to the Crash Site level. You need to find the two characters training with each other.
Afterwards, you need to hit them both at the same time to unlock the trophy.