_ o c k e t
fill in a "d" - If this is marked on the calendar, you might be in some trouble.
Dockets are related to (law) cases
fill in a "h" - Google picture of this, you'll find mostly music sheets and a kind of sport.
Hocket is a musical term
fill in a "l" - Open me and you'll usually find your beloved one.
locket holds a picture
fill in a "p" - It is believed that in some Asia country, this is where some monsters live.
Pocket monster! I choose you!
fill in a "r" - "Fly me to the moon, and let me play among the stars"
Rocket
fill in a "s" - You might feel your lack of power disturbing without me.
Socket, where you plug stuff in