Whenever I draw I tend to come up stories about the picture to help it evolve. This usually happens pretty naturally and of it's own will.
Here's the cliff notes;
Peach and Daisy are kidnapped, as usual, by that evil overgrown reptile we all know as Bowser. Mario and Luigi respond as we've come to expect, they attempt a rescue. However, in this retelling Mario doesn't survive the encounter, suffering a brutal death at the hands of Bowser. Luigi barely escapes with his life intact. Bowser, finally achieving his goal, goes into hiding with the two lovely ladies. Distraught and but not defeated Luigi spends several years and what cash he's saved from working as a plumber tracking Bowser. He never finds a solid lead. At the time of this photo it has been 15 years since Mario's death. Luigi has become listless and empty, only kept sane by his small private eye business, Daisy Detective Services.