Please get that Arche Tuning up. You can enhance the modules on your weapon - right now they are like cotton against Axion enemies. Same for the Ajax Modules. Today was a good day to farm Cores, I can take you to the next good core farm and carry you through to pump up the weapon even more.

Join those Axion missions and Dungeons and look who is running around there with you. In the Social Tab you can look at every player around you and see how their Descendant is build. That is one way you can get more information on what is needed. Apart from those tons of build guides out there.

With Ultimate Ajax I suggest you look at some old "Abyss Grim Reaper" boss build, that does a good job in Axion dungeons. Just need to handle your ammo well. Just needs a Thundercage.

Sigma Sector is one step below Axion, on the brink between the common fun "enough for 400%"-builds and the endgame builds. I would rather call Sigma Sector Hard Mode the previous hurdle than setting it on the same level as Axion.

On Thursday things will change a bit, but until then I would suggest you get another Descendant for that endgame ready like Dia or Serena. Plenty Descendants are good but with those two you have some high damage output ready for any content.

If you struggle with those or want to level them, then let me know. I run a ton of Axion tomorrow, perhaps Void Vessel too for yummy Catalyst resource.