Day 17 covers all of Chapter 12, Devadatta, and opens Chapter 13, Encouragement for Keeping this Sutra.

Having last month heard in gāthās of the king who sought the Great Vehicle, we learn who the seer was.

I sought the Great Dharma strenuously
Because I wished to save all living beings.
I did not wish to benefit myself
Or to have the pleasures of the five desires.

Although I was the king of a great country,
I sought the Dharma strenuously.
I finally obtained the Dharma and became a Buddha.
Therefore, I now expound it to you.

The Buddha said to the bhikṣus:

“The king at that time was a previous life of myself. The seer at that time was a previous life of Devadatta. Devadatta was my teacher. He caused me to complete the six pāramitās. He caused me to have loving-kindness, compassion, joy and impartiality. He caused me to have the thirty-two major marks and the eighty minor marks [of the Buddha]. He caused me to have my body purely gilt. He caused me to have the ten powers and the four kinds of fearlessness. He caused me to know the four ways to attract others. He caused me to have the eighteen properties and supernatural powers [of the Buddha]. He caused me to have the power of giving discourses. I attained perfect enlightenment and now save all living beings because Devadatta was my teacher.”

Here is Nichiren’s take on the king and seer from Minobu-san Gosho, Mt. Minobu Letter, Writings of Nichiren Shōnin, Volume 5, Pages 126-127

In another past lifetime of the Buddha he was the ruler of a great country because of the accumulation of virtue in the past. But he was neglectful in ruling the country. His 100 ministers and all the people revered him as a consequence of the pleasurable results of his former observance of the ten virtuous acts. But this would prove to be like the flame of a lamp flickering in the wind, or a dream on a spring night, or the brief blooming of morning glories on a bamboo fence. Though he had followed the virtuous precepts in his past lives, now that he had been born as the ruler of a great country he was enticed by the murderous demon of impermanence and spent his life in vain, neglecting to practice the good. [If he continued in this way] he would sink into the bottomless flames of the Hell of Incessant Suffering where there is no distinction between warriors and peasants. The flames of the three torments would scorch him, his five limbs would be bound in iron cords, and the gag of the three torments would be inserted into his mouth. The monstrous jailers of hell armed with tridents and screaming callously, would punish him by stabbing him all over his body. The sounds of his cries would reach up to the heavens, and in his grief he would fall to the ground. His 100 ministers and all his people would be unable to come to his aid, nor could his family and loved ones come to save him. [He thought of his beloved wife] with whom he slept and awoke on the same bed within the brocade curtains. Together they were like two birds with one wing each who must fly together in the heavens, or like two trees with branches intertwined on the earth. The days and months they had spent together had amassed into years, but not even she and their children could come to visit him. Reflecting on these things he opened his storehouses and donated gold and silver and all the seven treasures in order to support the saṃgha. He donated elephants and horses, and even his wife and children to them. Later he blew a conch seeking for the great Dharma. He beat a drum seeking for the great Dharma. He sought the Dharma in all directions. At that time there was a seer named Asita. This seer came to the king saying, “I can teach you the True Dharma if you are able to serve me well.” The king rejoiced and entered the mountains, where he collected fruit, gathered firewood, picked vegetables, and drew water for a thousand years. All the while he constantly recited, “Jōzon Myōhōko, Shinjin Mukeken,” which means, “Because I am seeking the Wonderful Dharma I do not feel tired in body and mind.” Through this practice he was able to obtain the Dharma of the five Chinese characters: myō, hō, ren, ge, and kyō. This king would become Śākyamuni Buddha in a future life. In our country there is a Japanese poem that tells how he received the Dharma by serving his master. When a sutra is copied and presented this verse is sung: “I obtained the Lotus Sūtra by gathering firewood, picking vegetables, and drawing water.” Hearing this I am overcome with emotion.