Here is the full list of all 12 Omega Five achievements worth 200 gamerscore. It takes around 4-5 hours to unlock all of the achievements on Xbox 360.
Complete Single Player Arcade Mode without continues using R.A.D.
Complete Single Player Arcade Mode without continues using Sensei.
Go 30 seconds without swinging Sensei's sword.
Complete Single Player Arcade Mode without continues using Tempest.
Repel 20 or more enemy bullets using Tempest.
Complete Single Player Arcade Mode without continues using Ruby.
Clear Stage 4 in Single Player Arcade Mode.
Clear Stage 3 in Single Player Arcade Mode.
Clear Stage 2 in Single Player Arcade Mode.
Held onto an enemy for 10 seconds or longer with the anchor using Ruby.
Cleared Stage 1 in Single Player Arcade Mode.
Maintained the max. bonus for 30 seconds or more.