I must catch the female pikachu/raichu with light ball or give it to hold in the day care?
To breed a pichu with v-tackle you need to get a light ball which can be obtaind on soul silver only by pokewalker on the yellow forest so too late
but theres 5% that a wild pickachu can hold it yet its very rare
anyway if you will obtain it somehow put it on a male ! pickachu or raichu and breed it with ditto or a female pickachu
To get a pichu with volt tackle you catch a wild pickachu holding a light ball and then give it to either the male or female pokemon you have in the daycare pickachu is in the fairy group