It's Easy.All you have to do is follow these steps and pikachu will be happy just after you defeat Gary's Eevee .
Step 1: Start a new game and then take the potion.
Step 2: Go to The wild and watch as Prof.Oak captures Pikachu.
Step 3: Go to Prof.Oak's Lab and watch as Gary pushes you and takes Eevee.
Step 4: You must defeat Gary's Eevee and use the potion 5 times on Pikachu.
Step 5: Pikachu will be happy with you.
Chat with our AI personalities
Once Pikachu is happy with you, talk to the lady next to the gym in Cerulean City. She will give you a Bulbasaur.
In Cerulean City, A stretched house with a Bulbasuar next to a lady. Talk to her. (She will only give it to you if your Pikachu is happy enough)
A woman in the house West of the Cerulean City Pokemon Centre will give you a Bulbasaur if your Pikachu is happy enough. The Bulbasaur is level 10.
Pichu comes before Pikachu. Pichu evolves into Pikachu when its uber happy followed by Raichu with a thunder stone.
you have to make it happy you can do this by massages and giving it proteins you evolve pichu with happiness and freindship.you can also give him beris that make it frendlier