I'll help you out since not only do I like Pit, but I also hate Pikachu.
Use Angel Ring or Mirror Shield (I prefer Mirror Shield) to reflect Pika's Thunder Jolts (the neutral B). Sometimes, use arrows in close range for a simple hit if the Pika player is not aware of it. Aim the arrows towards the ground with precision to hit the crawling Pika.
Pika's FSmash is a pain, but you can sidestep it. Or... use the Mirror shield as an offensive weapon and the part where the Mirror shield shines, when Pika hits it, he will turn the other way, similar to Mario's cape, then go in to attack.
If the annoying Pika loves to do that Electric spin thing (Dsmash), try keeping a short distance from him and then attack him.
If you get Pika off the stage, try to fly towards him and use F-air or B-air to try and kill him, but not all the time, because he might just use quick attack to avoid you.
If you get knocked off the stage however, I'm aware that some Pika players love to use thunder by the edge. If Pika allows himself to get hit by his thunder at the time, you could somehow take advantage of it. Get Close to Thunder's location, Use Angel Ring (this is a reflector too) or Mirror Shield, but i recommend Mirror shield.
When the shield hits thunder, "Nice Try" and Pika damages himself with thunder while that thunder you reflected is harmless to you. This means you can't glide to do this, just use your 3 jumps slowly and carefully close to Thunder to perform this.
Try this trick vs Thunder against a Lv 9 Pika at Final Destination. You'll see that my strategy works here, and should work against others. Note: If thunder strikes in the middle of Pit,, the shield will just block it, no reflect.
Because of thunder, I dont think Gliding will be useful against the yellow rat, except flying under the stage and to the other side.
Predict the moves Pika will do to you at each situation, counter it, and you will achieve victory.