A picture's worth a thousand words and is also a great way to prove a point and get unknown facts straightened out. Here's proof that Pachirisu's a girl. There's a picture of Pachirisu from the episode "Tanks for the Memories". In that episode the gang stopped at a cafe where Brock was helping one of the waitresses bond with her Miltank, Ilta. While Brock helped her, Dawn, Ash and their Pokemon helped the other two waitresses inside the cafe during rush hour. One of the pictures below is from that episode. It's Pachirisu, Buneary, and Ambipom all wearing waitress outfits, and they all look super excited, as did Dawn. Now, think about how Ash, Pikachu, Piplup, and Turtwig looked, embarrassed, right? Exactly, and if Pachirisu were a guy, it's seguro to say Pachirisu would've been embarrassed as well. Also, I have another picture of Pachirisu in a cheerleader outfit, and Pachirisu looks excited, and that probably wouldn't be the case if Pachirisu was a male.