Multiple Graphics for 2D Game

Behind asking question my target is to cover as much devices as possible by giving best result to them. I want to create game like that each game player feels that this game made for him only. So I have to cover more aspect ratio in creating game.

Already I ask following question to solve this problem using single graphics but I didn't get desire result. Targeting Multiple Display Resolution

After reading some forums and tutorials related to this topic I found that to create a game which runs without creating any black or blue bars, I have to use multiple graphics. So my question is how to use multiple graphics in unity 2d?

Althouth 2D Tool Kit has some strategy regarding use of multiple graphics but at present I am developing game with unity 2d not using any third party content.

If any person has better idea regarding this then please share with us.