I saw this anime in the late '90s on TV, but I believe it's from 80's. Boy summons or controls robot with a knife (seems it was combat-like knife, Ka-Bar or similar). But inside of that knife is some kind of complicated control device. And then that boy fights with some kind of invader robots in space. And obviously some bad guys try to dissect that knife and gain control of robot.
I understand that's not the clearest description, but it was more than 20 years ago. This anime is bugging me from time to time, so I hope someone could help me to identify it.