Here is the full list of all 36 Procyon achievements.
Kill 20,000 enemies
Complete Stage 3
Block 500 bullets with the shield
Destroy all of the large armada ships in Stage 3 on Normal difficulty or higher
Sustain a multiplier of 500x for 30 seconds
Complete any stage without using the shield
Destroy 50 enemies with one lightning charge
Kill 3000 enemies
Complete any stage without using bullets
Destroy 1000 enemies using the beam
Complete any stage without using the beam
Complete Stage 2
Block 50 bullets with a single use of the shield
Destroy 1000 enemies using the bullets
Retry from the Game Over screen
Reach the boss of a stage without firing any weapons
Reach the boss of a stage without firing any weapons, using any shields, or dying on Normal difficulty or higher
Complete Stage 1
Achieve a multiplier of 500x
Complete Stage 4
Complete Stage 5
Complete all stages on Easy difficulty (or higher)
Complete all stages on Normal difficulty (or higher)
Complete all stages on Hard difficulty
Complete Stage 3 in Attrition mode
Complete Attrition mode on Easy difficulty (or higher)
Complete Attrition mode on Normal difficulty (or higher)
Complete Attrition mode on Hard difficulty
Complete Stage 3 in Survival mode
Complete Survival mode on Easy difficulty (or higher)
Complete Survival mode on Normal difficulty (or higher)
Complete Survival mode on Hard difficulty
Keep the beam locked continuously on a single enemy for 30 seconds
Lose your last life during the final boss battle
Lose a life to the first enemy of the first stage
Complete Stage 4 without shield-blocking or being hit by any purple homing bullets on Normal difficulty or higher.