For both the mother ad father, you would give the Pokemon with the nature you want an everstone.
If youre playing a game that came out before Black2/White2, you don't have a full chance of passing down the nature. It's a 50% chance, so try again.
If you're not playing an older game, the only thing I can think of is if you accidentally gave the everstone to the wrong Pokemon (in this case the father), or you hatched an egg that was made before you gave pikachu an everstone. Double check that your everstone is on the right Pokemon and try again. This should clear up any problems.