If you want to combine silliness and seriousness in one, I highly recommend you research Key Visual Arts and some of their works. They produce visual novels which have done so fantastic at evoking emotion that they have been labelled "crying games". They use a specific formula which is made to really hit home hard. By starting the story in a very silly and happy-go-lucky method, you are little more attached to these characters and you are used to seeing these characters happy. Then you make a HUGE turn. That jump from silly to serious, if done right, can completely destroy the player's emotions. After seeing these characters go from always happy and smiling, to crying,dying and being downright depressed, the player will react with a wide variety of emotions, including sadness and sympathy. Like a guy earlier said, check out Angel Beats, that is a work by Key. But also check out the anime Clannad as well, along with the Visual Novels Little Busters and Rewrite. These all perfectly portray what you're trying to do.
Hope this helps!
This post has been edited by Seano299: Dec 26 2012, 05:53 AM