Naiin was the seal for emperors with the inscription 'Tenno Gyoji' (seal of the emperor) on it; it was three square sun and used for iki (a letter of appointment) of officials higher than Goi (fifth rank) and the official documents given to provinces.
内印は天皇の印章であり、印文は「天皇御璽」で大きさが方3寸と決まっており、五位以上の位記および諸国に下す公文に用いた。