Short answers, pulled from the story.
Sentient beings in Buddhism refers to all living, conscious creatures subject to illusion, suffering, and rebirth in samsara. The term translates several Sanskrit words including jantu, jagat, and sattva, and broadly designates the audience and object of Buddhist teaching.
The five aggregates, or skandhas, are matter, sensation, perception, mental formations, and consciousness. In the Samyutta Nikaya, the Buddha compares the assembled aggregates to a chariot: just as "chariot" names an assembly of parts, "being" names the collection of these five components.
Early Buddhist sources classify sentient beings into five categories: divinities, humans, animals, tormented spirits, and denizens of hell. Some traditions add a sixth category, the asuras, placed between divinities and humans.
Dogen wrote that "those who greatly enlighten illusion are Buddhas; those who have great illusion in enlightenment are sentient beings." This formulation defines sentient beings primarily as those who have not yet attained awakening.
In Mahayana Buddhism, Buddha-nature is the intrinsic potential within sentient beings to transcend samsara and attain Buddhahood. Sentient beings are the object of the bodhisattva vow and of maha karuna, great compassion, precisely because they carry this potential.
Zhanran, who lived from 711 to 782 and belonged to the Tiantai school in East Asian Buddhism, formally defended the Buddha-nature of inanimate things. Japanese figures Kukai and Dogen also advanced similar positions.