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 安全 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.

Come little children, come with me
安全 and happy 你 will be
Away from your homes, now let us run
With Hypno, you'll have so much fun

Oh, little children, please don't cry
Hypno wouldn't hurt a fly
Be free, be free be free to play
Come down in my cave with me to stay

Oh, little children, please don't squirm
Those ropes, I know, will hold 你 firm
Hypno tells 你 this is true
But sadly, Hypno lied to 你
Oh, little children, 你 mustn't leave
Your families for 你 will grieve
Their minds will unravel at the seams
Allowing me to haunt their dreams

But surely, all of 你 must know
That it is time for 你 to go
Oh, little children, 你 weren't clever
Now 你 shall stay with me forever