You can unlock additional characters and costumes in Raid mode if you satisfy the corresponding requirements, as indicated below.

Costume	How to unlock
Chris Redfield (Sailor)	Deal 100,000 damage with one shot.
Chris Redfield (Wetsuit)	Reach Level 30.
Clive R. O'Brian	Reach Level 20.
HUNK	Earn an S rank on every stage on the "Abyss" setting.
Jack Norman	Beat every stage on the "Abyss" setting.
Jessica Sherawat (Terragrigia)	Reach Level 40.
Jessica Sherawat (Wetsuit)	Beat every stage on the "Trench" setting.
Jessica Sherwat (Snow)	Beat every stage on the "Chasm" setting.
Jill Valentine (Beach)	Acquire a super-rare weapon.
Jill Valentine (Pirate)	Beat the "Ghost Ship" bonus stage.
Keith Lumley (Casual)	Earn an S rank on every stage on the "Chasm" setting.
Keith Lumley (Ninja)	Reach Level 50.
Keith Lumley (Snow)	Beat Episodes 4 through 6 in Campaign mode.
Morgan Lansdale	Earn an S rank on every stage on the "Trench" setting.
Parker Luciani (Beach)	Acquire 10 total bonuses in Raid Mode.
Parker Luciani (Terragrigia)	Beat 10,000 enemies.
Quint Cetcham (Casual)	Acquire every super-rare weapon.
Quint Cetcham (Snow)	Reach Level 5.
Rachael Foley	Receive the "Trinity" bonus for the first time.
Raymond Vester	Reach Level 10.