How do you make a Pikachu happy in Pokemon yellow virson?

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.