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?"
You:  "Stop!"

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.