If I have more than one {L} Energy attached to Raikou, does its "Shining Body" Ability reduce the damage done to it by 20 for each {L} Energy?
No, you only get a maximum of 20 damage reduced from this Ability.
Source: BREAKthrough FAQ (2015-11-19), TPCi Rules Team (2015-11-19)

Relevant cards

Note: All applicable cards may not be listed below.
XY8_55