The Thirteen Buddhas is a Japanese grouping of Buddhist deities, particularly in the Shingon sect of Buddhism. The deities are, in fact, not only Buddhas, but include bodhisattvas and Wisdom Kings. In Shingon services, lay followers recite a devotional mantra to each figure, though in Shingon practice, disciples will typically devote themselves to only one, depending on what the teacher assigns. Thus the chanting of the mantras of the Thirteen Buddhas are merely the basic practice of laypeople.
The Thirteen Buddhas are also an important part of a traditional Japanese Buddhist funeral service, with each deity having a corresponding memorial service for the deceased. The thirteen in Japanese and Sanskrit and the corresponding date of their service after the death are:
Fudō (Acala), 7th day
Shaka (Sakyamuni), 14th day
Monju (Manjushri), 21st day
Fugen (Samantabhadra), 28th day
Jizō (Ksitigarbha), 35th day
Miroku (Maitreya), 42nd day
Yakushi (Bhaisajyaguru), 49th day
Kannon (Avalokitesvara), 100th day
Seishi (Mahasthamaprapta), 1st anniversary
Amida (Amitabha), 2nd anniversary
Ashuku (Akshobhya), 6th anniversary
Dainichi (Vairocana), 12th anniversary
Kokūzō (Akasagarbha), 32nd anniversary
While the thirteen figures have several mantras associated to each respectively, those listed below pertain to the standard formula used in Japanese ritual. The Shingon and Tendai schools each use a different method of transliteration of the original Sanskrit. Bhaisajyaguru is the only figure whose mantra fundamentally differs between traditions.