Interesting how the form with the creepiest origin/use provides peace of mind, while the form representing two people joined in Love resonates destruction (which, provided more destruction isn't hurling your way as it so often is, provides peace of mind).
But everything offers destruction followed by peace of mind!
Basic Form: Destruction of braincells; peace of mind with shield.
Energy: Destruction through energy shots; peace of mind with no enemies.
Beast: Destruction of poor, innocent animals; peace of mind of getting their ammo.
Plant: Destruction with death pillar of plant; peace of mind of quick transportation.
Sun: Darkness; being able to see.
Fishy: Your size; being able to squeeze through stuff.
Spirit: Bullets, bullet-free-ness and a break in action.
Dual: EEEEEEEEEEEEEEEEEEEEEEEEEEEEEE; no enemies.
Li Song: Loneliness; company.
Shield: Vulnerability; protection.
The Verse: Being frustrated with not being able to play it; finally figuring it out.
Race Song: Boredom; a break from the action present in the rest of the game.
Whale Song: The abyss; nom nom nom.
See? ^^