Unlockables - Complete each achievement to get the allotted gamerscore.

"R.A.D" Master (25) Complete Single Player Arcade Mode without continues using R.A.D.
30 Second Max. Bonus (15) Maintain the max. bonus for 30 seconds or more.
Cleared Stage 1 (10) Clear Stage 1 in Single Player Arcade Mode.
Cleared Stage 2 (10) Clear Stage 2 in Single Player Arcade Mode.
Cleared Stage 3 (10) Clear Stage 3 in Single Player Arcade Mode.
Cleared Stage 4 (10) Clear Stage 4 in Single Player Arcade Mode.
Don't Let Me Go (15) Hold onto an enemy for 10 seconds or longer with the anchor using Ruby.
Incredible Restraint (15) Go 30 seconds without swinging Sensei's sword.
Ruby Master (25) Complete Single Player Arcade Mode without continues using Ruby.
Sensei Master (25) Complete Single Player Arcade Mode without continues using Sensei.
Tempest Master (25) Complete Single Player Arcade Mode without continues using Tempest.
Untouchable (15) Repel 20 or more enemy bullets using Tempest.

There are a number of unlockables after satisfying game conditions. These can be unlocked by continuing, and I'm not sure if you need to finish the game using the same character throughout but it's the safest choice.

5 credits Play for 60 minutes total
8 credits Play for 180 minutes total
Arcade Mode ++ Complete Arcade Mode
Challenge Mode Complete Arcade Mode
Challenge Mode ++ Complete Arcade Mode
Character - R.A.D Complete Arcade Mode using Ruby
Character - Sensei Complete Arcade Mode using Tempest
Extra Credits As gameplay time elapses. 5 credits at 60 minutes
Female System Voice Complete Arcade Mode using R.A.D
Retro Mode Complete Arcade Mode using Sensei
Unlimited credits Play for 300 minutes total