Diomedes will appear in the Astral Chain file 3, just after you got it out of the astral plane and saved the civilians. He is armed with a huge sword that he can be very difficult to dodge, so in this fight, you will want to keep your distance.
Astral channels: how to beat Diomedes
Diomedes is armed with a massive sword which he balances in huge arcs, which makes him difficult to dodge. He is also inclined to make several rotating attacks, moving into the small arena as a whirlwind. The best way to fight this boss is to keep your distance. You will want to keep your legion at the top of the astral chain, leaving it to act on DIOMEDES while you are in a safe place.
The best thing to do is try to operate from the center of the small arena in which you are fighting. Diomedes can go fast and cover a lot of terrain when it makes its rotation attacks, so be sure not to be stuck in a corner where it will easily kill you.
Use the gun mode of your weapon to hit it with combos and synchronization attacks. Diomedes will make an attack from top to bottom with her sword, which will cause an explosion of massive energy. Dodge away, dodge quickly rolls towards him. You should be able to get two to three Slash attacks with your legion before having to go back.
You want to repeat this tactic over and over again, but be very careful. If you encounter more serious difficulties, Diomède will strike you each time for about a third of your health. Therefore, being taken in one of his combos means death. You will also have to constantly move your legion to the combat zone, because if you leave it too close to Diomes too long, it will simply be knocked out and postponed, which will reduce the damage you are undergoing.
The best thing to do with Diomedes is simply to play safely, to operate from afar and to reduce it slowly until you beat it. And don’t forget to get a last blow at the end to get the maximum genetic code of this annoying boss.