If a major evil demon of fundamental darkness can enter the body of even a bodhisattva on the rank next only to the Buddha, preventing this bodhisattva from attaining the merit of Enlightenment of the Lotus Sūtra, all the more so can this demon wreak havoc with beings below the bodhisattva rank. Also, the King of Devils in the Sixth Heaven can occupy the body of the wife and children to fool the parents and husband, enter the body of the king to persecute the practicer of the Lotus Sūtra, or go into the bodies of the parents to torture their filial children.
When Śākyamuni Buddha was the Crown Prince Siddhārtha, he sought to abdicate his princely position in order to enter the priesthood. King Śuddhodana, however, advised the Prince to refrain from entering the priesthood until his pregnant wife gave birth to their son Rāhula. The King of Devils postponed the birth of Rāhula for six years in order to prevent the Crown Prince from entering the priesthood.
Kyōdai-shō, A Letter to the Ikegami Brothers, Writings of Nichiren Shōnin, Volume 6, Followers I, Page 76