http://www.ludomancy.com/blog/2008/09/03/i-wish-i-were-the-moon/

"Tragedy": Drop any of them into the water
"Bring me the Moon": Get the "Lost Love Ending", then give the small moon to the boy
"Lost Love Ending": Sit the boy in the boat and wait until the moon is gone
"I am your Moon Ending": Sit the boy in the boat and the girl in the moon
"Seagull Trip Ending": Sit both the boy and the girl over the gull. Be sure to put both of them. One will not suffice.