I started to read this, and something became very noticeable to me. It was very confusing to keep in mind what was going on and who it was happening to. For instance, in the beginning scene, it took a little bit to figure out that Richie is the Raichu and Sparky is the Pichu.
Narration is what you need more of. Instead of your story being mostly dialogue, include more descriptions of what the characters are doing as they talk. Like when Sparky is "furious-looking", show that he is by his paws clenching or having him glare at Richie.
Also, some more back story about the characters. Like how did Sparky meet Richie, or how did Richie become a Gold Ranked Rescue Team Leader. And where did Garchomp come from and why does he have it out for Richie?
Same with the battle scene. Describe the attacks more. How did Garchomp manage to slash Richie deep enough to kill him (and how did Richie not even notice it?) Why didn't Richie, an experienced fighter, not expect Garchomp to use Dig? How does Sparky feel to watch his hero die?
Taking the time to describe the world your story's in, what the characters are doing, who the characters are, and how the characters feel make your story more real in the reader's mind.
Keep writing and good luck!