For the best ending, give these responses to Mae when you meet her in the Lost Forest:
Mae: "If I stay here I'll be safe, right?"
Mae: "Why do you fight?"
You: "For everyone."
Mae: "Why must you live?"
You: "For finding the answer."
Step 1: Talk to the teacher in the room north of the entrance.
Step 2: Search all the rooms on the 2nd floor.
Step 3: Talk to the students in room 2-1.
Step 4: Go to the casino in Joy Street and talk to everyone there.
Step 5: Visit the abandoned factory.
Step 6: Go to Yin & Yan and talk to Chris's mother. Tell that you know Chris and that you will be his friend.
Step 7: After leaving the hospital, meet Chris in front of the Sebec Building.
Step 8: Do NOT allow Brad, Ellen, or Alana to travel with you.
When you meet Chris in Mary's World, he will join you.