My Six Girlfriends

Asahi Sawamura stood in front of his parent's graves, blaming himself for his parent's death. He kept saying sorry to them when a sweet voice sounded,

"You want to revive them?"

Asashi was confused but nodded.

"Allright, then I will fulfill your wish, but in exchange, you must do something. If you aren't able to do it, then your parents will die again."

Asashi wondered what he'd have to do to keep his mother alive and revive his father.

[Asahi Sawamura, you have to make these six girls yours. You can use whatever methods you want to. If you aren't able to make them your girlfriends before you graduate high school, then your mother will die. If you are able to do it, then I will revive your father]

[All six of them have to be your girlfriends when you graduate]

How will Asashi complete this mission? Can he make these six his girlfriends without them finding out about one another? What if they discover Asashi is cheating on them? How will he handle it?