Obviously, there are SPOILERS ahead.
I've gotten several messages lately about how to get certain endings, so I created a brief guide to help players along with what I feel is the most difficult to attain.
Getting the Lexus Ending: http://www.crestfallen.us/lexus.html
For more details, I'd advise consulting this more thorough guide. It shows you exactly what things will affect your relationship points with Lexus.
http://jeramyu.homestead.com/files/way_faq.txt