The Object of Devotion of the Nichiren School, the Pure Land School, and the True Word (Shingon School).

From concluding diagram of Nichiren's important writing, The "Rooster" Diagram:

Object of devotion of the T’ien-t’ai (Nichiren) School school, the Thus Come One Shakyamuni as the Buddha who actually carried out practice and achieved enlightenment in the inconceivably remote past

Vairochana of the Flower Garland school, Mahāvairochana of the True Word school, and other Buddhas are all followers of this Buddha.

Manifested body Buddha has a beginning and has an end (Shakyamuni Buddha of India of the Dharma Characteristics and Therevadan schools)

Reward body Buddha has a beginning but no end (for example Amida of of the Pure Land School)

Dharma Body Buddha has no beginning and has no end (for example Mahavairochana of the True Word or Shingon school).

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Three bodies attained in the remote past as the Object of Devotion of the Tientai and Nichiren School... Manifested Body, Reward Body, and Dharma Body, all having neither beginning nor end

"When the Flower Garland and True Word schools speak of the three bodies that have no beginning and have no end, they are stealing the terminology of the T’ien-t’ai school and applying it to the sutras that are the foundation of their own schools." - Nichiren

Specifically, Nichiren is referring to Shakyamuni Buddha of the Juryo Chapter, Generally he is referring to each of us. This is the rational for attaining Buddhahood in this very body. In a sense, as RonnyMarch asserted, we could say (generally) that it refers to the body of believers. However, as in the discussion of Nichiren's problematic works, Mr. Lamont is correct, Shakyamuni Buddha of the Juryo Chapter of the Lotus Sutra is a very real Buddha (Ji Butsu) possessing three bodies. As we learned in the 16 th Chapter, this Buddha can take on many forms (eternal Manifested Body) and does indeed have "a concrete or tangible character (gutaikaku) or eternal Reward Body. as Nichiren stated in the beginning, He is the Object of Worship of the Tientai and Nichiren sect. The community of believers, also possessing the Three Bodies is the Treasure of the Sangha.