Ummm....
Basically, he's the main protagonist out of D/P/Pt's little brother. Their father dissapeared whilst researching Rayquaza, so he's been tracking it down.
He meets the protagonist out of this game, and, being upset because of the nature of his journey, battles him, thinking he's after Rayquaza. In the end, they track down Rayquaza.Then they have a battle beforehand, in which he leaves the protagonist with only 1 pokemon, and no bag (no pokeballs). Then lets him battle Rayquaza.He loses.Diamond turns up on my guy's Garchomp, swaps it for my his Togekiss, which my guy was holding.He also brought a masterball. Garchomp blocks him from throwing the masterball, as Diamond also came to tell him they've found Jirachi, which can bring their dad to them, when it appears on an island in 7 days (the island is based on St. Michael's Mount, near Cornwall). I then catch Jirachi, and use it to bring back dad. Then there's this quest involving finding two feathers, to summon Celebi, to send the protagonist back in time, to stop Silver stealing a special Phione egg that knows a special version of Dive.Once back in the present, the egg will hatch after 40,000 steps, enabling him/her to go to this deep cavern where Rayquaza is.
However, I haven't had a reply about the bit involving Celebi, so that'll probably not happen.