DPA001: In Search of the Legendary Pokémon Dialga!!

In Search of the Legendary Pokémon Dialga!! (神話のポケモンを求めて!!) is the 1st chapter of Volume 1 of the Pokémon Diamond and Pearl Adventure! manga.

Synopsis
Hareta, a young boy, lives in the forest when one day, Mitsumi visits him. While playing with the Pokémons, he angers an Onix and starts to attack him. He receives his first Pokémon, Piplup. When Hareta and Mitsumi are ready for their journey, the very same Onix starts to attack them...

Chapter Plot
Mitsumi cycles through the forest, searching for boy she is looking for. Suddenly, a horde Aipom appear and run over Mitsumi. Looking at the horde, Mitsumi finds the boy she is looking for, Hareta. Once they finally see each other face to face, Mitsumi introduces herself to Hareta and reveals to him that she is the assistant of Professor Rowan. After the meeting, she is surprised how good Hareta can interact with the Pokémons. Hareta tries to lift up a rock but the rock was actually a part of an Onix, who gets angry. Mitsumi orders Hareta to choose a Poké Ball from the case she brought along. He chooses a Poké Ball but doesn't know how to open it and bits on the Poké Ball. The Poké Ball opens and Piplup is the Pokémon he chooses but Piplup is stuck in his mouth as the Poké Ball opened in his mouth. When spitting Piplup out, Hareta orders Piplup to attack but Piplup doesn't listen to him, so Hareta attacks Onix himself but failed.

Professor Rowan appears and reveals Hareta's past to Mitsumi. Mitsumi is suprised by his past and asks Hareta if he wants to see the legendary Pokémon Dialga, in which Hareta agrees and decides to go with her on a journey to see it. Hareta gets his traveling clothes and once Hareta and Mistumi are outside, the same Onix, who Hareta angered before, attacks them. Hareta states that the Onix isn't itself and that it is out of control. Hareta orders Piplup to attack Onix, but it still refuses to listen to him. When Piplup is in danger, Hareta saves it and said to Piplup if he doesn't want to battle, that it was fine. Hareta himself charges at the Onix and tries to bring Onix back to its old self. Piplup sees Hareta and what he is doing and runs towards Onix aswell. Both are convinced to take Onix down and Hareta orders Piplup to use Bubblebeam, which is really powerful and surprises Mitsumi. Onix is blasted into the river and is back to its old self. After seeing what Hareta has done, Mitsumi eventually believes that Hareta will meet Dialga and before Hareta and Mitsumi go on their journey, Hareta receives his Pokédex from Professor Rowan.

Debuts
Human
 * Hareta
 * Mitsumi
 * Prof. Rowan

Pokémon
 * Piplup (Hareta's)
 * Starly (Mitsumi's)

Move
 * Bubblebeam