The following are unlocked in stages by collecting ALL 5 keys and then unlocking the corresponding 5-keyed door.

Unlock 3 Extra Lives:
In The Ark get ALL 5 keys

Unlock 2 Turrets:
In Black Comet find ALL 5 keys

Unlock Turrets:
In Final Haunt find ALL 5 keys

Unlock Armored Car:
In Lost Impact find ALL 5 keys

Unlock Black Volt:
In Sky Troops find ALL 5 keys

Unlock Warp Hole:
In Death Ruins find ALL 5 keys

Unlock Warp Hole:
In Space Gadget find ALL 5 keys

UnWarp Portal:
In The Last Way find ALL 5 keys

Unlock Shortcut:
In Cryptic Castle find ALL 5 keys

Unlock Black Hawk:
In Glyphic Canyon find ALL 5 keys

Unlock Air Saucer:
In Lava Shelter find ALL 5 keys

Unlock Air Saucer:
In Central City find ALL 5 keys

Unlock An Air Saucer:
In Air Fleet find ALL 5 keys

Unlock Armoured Car:
In Westopolis find ALL 5 keys

Unlock GUN Vehicle:
In Lost Impact find ALL 5 keys

Unlock Milatary Vehicle:
In GUN Fortress find ALL 5 keys

Unlock Tank Cannon:
In Prison Island find ALL 5 keys

Unlock Tank Cannon:
In Iron Jungle find ALL 5 keys

Unlock Black Arm's Vehicle:
In Sky Troops find ALL 5 keys

Unlock Black Arm's Vehicle:
In Glyphic Canyon find ALL 5 keys

Unlock Large GUN Cannon:
In Lethal Highway find ALL 5 keys

Unlock Warp Hole:
In Digital Circuit find ALL 5 keys

Unlock Extra Shooting Gallery:
In Circus Park find ALL 5 keys

Unlock Alternate path to a Red Terminal:
In Mad Matrix find ALL 5 keys

Unlock Switch that makes Ring Trails to the end of the Level:
In Cosmic Fall find ALL 5 keys

Opens Cage which triggers Shortcut to the end of the Level:
In The Doom find ALL 5 keys

Unlock Expert Mode:
Get ALL 71 'A' rankings.

Unlock Last Story:
Beat every 6th stage in Story mode to see the Hero and Dark endings for each. There are 10 endings in total.

Unlock Hidden Key Bonuses:
Get ALL 5 keys in stages, they are located behind the 5-keyed doors.

Unlock 2 Turrets:
Get ALL 5 keys in Black Comet

Unlock 3 Extra Lives:
Get ALL 5 keys in The ARK

Unlock Armored Car:
Get ALL 5 keys in Lost Impact

Unlock Black Hawk:
Get ALL 5 keys in Glyphic Canyon

Unlock Black Volt:
Get ALL 5 keys in Sky Troops

Unlock Turrets:
Get ALL 5 keys in Final Haunt

Unlock Warp Hole:
Get ALL 5 keys in Space Gadget

Unlock Warp Hole:
Get ALL 5 keys in Death Ruins

Unlock Warp Portal:
Get ALL 5 keys in The Last Way

Unlock Extra Shooting Gallery:
Get ALL 5 keys in Circus Park

Unlock Large GUN Cannon:
Get ALL 5 keys in Lethal Highway

Unlock Shortcut:
Get ALL 5 keys in Cryptic Castle

Opens Cage which Triggers Shortcut to the End of the Level:
Get ALL 5 keys in The Doom

Switch that makes Ring Trails to the end of the Level:
Get ALL 5 keys in Cosmic Fall

Alternate Path to a Red Terminal:
Get ALL 5 keys in Mad Matrix


Unlock Hidden Vehicles

Unlock Air Saucer:
Find the 5 keys in Lava Shelter

Unlock Air Saucer:
Find the 5 keys in Central City

Unlock An Air Saucer:
Find the 5 keys in Air Fleet

Unlock Armoured Car:
Find the 5 keys in Westopolis

Unlock Black Arms Vehicle:
Find the 5 keys in Glyphic Canyon

Unlock Black Arms Vehicle:
Find the five keys in Sky Troops

Unlock GUN Vehicle:
Find the 5 keys in Lost Impact

Unlock Milatary Vehicle:
Find the 5 keys in GUN Fortress

Unlock Tank Cannon:
Find the 5 keys in Prison Island

Unlock Tank Cannon:
Find the 5 keys in Iron Jungle

Unlock Warp Hole:
Find the five keys in Digital Circuit


Unlock Level 2 Weapons:
Complete the corresponding storylines twice doing both Dark and Hero endings. The weapons you received will become Level 2.

Level 2 - Samurai Blade:
Pure Evil

Level 2 - Egg Vacuum:
Neutral

Level 2 - Satellite Laser:
Slightly Evil

Level 2 - Omochao Gun:
Slightly Good

Level 2 - Heal Gun:
Pure Good