As you’re wrapping up File 04 in Astral Chain, you will finally come across Jena Anderson that you’ve been after for most of the File. While technically Homunculus Alpha isn’t actually part of the first fight with her, we’ll include that as well since it’s pretty simple as an intro to the final boss of the File with Homunculus Alpha.
When you catch up to Jena, you will start a fight with her along with some help from Akira. The key here is to bind her with your Astral Chain and keep smacking her over and over again. There’s no real point to even look at her health, because it will quickly transition to a cutscene and she will escape while leaving you to fight Homunculus Alpha.
This big beast is easily the largest chimera you have fought in the game so far. He dangles down from the ceiling, with two legs that are to the side and can cause you trouble. The strategy for this fight is to use your Legion to bind each leg using your Astral Chain. Thankfully these stay binded for awhile each if it takes you some time to get the second one wrapped up.
Once both are wrapped up, you can much more easily attack the head of Homunculus Alpha or you can attack the legs as well if you wish. At some point he should fall over and let you deal even more damage.
Eventually, his legs will fade away with enough damage is done and he will change his attack patterns. Even with this, you shouldn’t have too much trouble. Try to stay down in the very middle under the head the best you can and just keep dealing damage. He shouldn’t have much health left at this point, so take him out as quickly as you can to end File 04.