This drama was so full of lovely things. I also appreciated the snippets of classical Chinese literature that were woven into the dialogues.  Among those, the lines from poems. Everyone in China or interested in Chinese culture knows a small or large selection of those, often inspired by the moon, that is so important in the cosmology and seasons following each others like waves, growing bigger and stronger through the force of attraction from the heavenly body, while everything falls in order and yearning finds its paths to completion. 

Here is the poem about yearning that Toutou was thinking about in ep. 39   12:08:

望月懷遠 (張九齡)              Wàngyuè huáiyuǎn (Zhāng Jiǔ Líng)    

                                                                                                             Far from your embrace, in the full moon     
           
            海上生明月,              hǎishàng shēng míngyuè,               The bright moon rises over the sea,
            天涯共此時。              tiānyá gòng cǐ shí.                                The end of the world is at this time.
            情人怨遙夜,             Qíngrén yuàn yáo yè,                         The lover complains about the night,
            竟夕起相思。               jìng xīqǐ xiāngsī.                                   Feeling lovesick is worst at night.
            滅燭憐光滿,            Miè zhú lián guāng mǎn,                  Blowing out the candles, yearning for light,
            披衣覺露滋。               pī yī jué lù zī.                                         Fastening the gown against the foggy dew.
            不堪盈手贈,             Bùkān yíng shǒu zèng,                     Overwhelmed by all the gifts,
            還寢夢佳期。                hái qǐn mèng jiāqí.                           It's also a good time to sleep and dream.

                                                                                  This is my humble understanding of the lines; here is another:

                                         Viewing the Moon, Thinking of You (Zhang Jiu-Ling, 678-740 AD, China)
                                                                                                                                                                                Ying Sun    © 2008
            As the bright moon shines over the sea,
            From far away you share this moment with me.
            For parted lovers lonely nights are the worst to be.
            All night long I think of no one but thee.
            To enjoy the moon I blow out the candle stick.
            Please put on your nightgown for the dew is thick.
            I try to offer you the moonlight so hard to pick,
            Hoping a reunion in my dream will come quick.

(Ying Sun is a Taiwanese guitarist who translated 24 poems to be set to music as a suite of 24 classical-guitar pieces titled the Grand Music of Tang, on music composed by Ssu Yu Huang and commissioned by classical guitarist Kazuhito Yamashita. This modern music can be listened to on this link to a live concert recording of 2000. The material "can be used for educational or noncommercial purposes with a reference to this website" : I recommend reading the 24 poems which are grouped in 4 categories : Nature ; Wine and Friendship ; Music ; Mood. They are part of a 50+ selection from the finest Tang poets, and are a nice introduction to the feel of classical Tang poetry)

About the poet : In the 21st year of Emperor Xuanzong of Tang Dynasty (733 AD), Zhang Jiuling served as prime minister. After being slandered by the traitor Li Linfu, he was demoted and sent away to serve as  Governor of Jing  in the 24th year of Kaiyuan (736). The poem "Wangyue Huaiyuan" is believed to have been written after this event. According to the "Old Tang Book" records, after Zhang Jiuling was ousted from court, Xuanzong still remembered Zhang Jiuling as an upright and generous prime minister. Whenever a minister recommended talents to him, Xuanzong would ask: "How is this person better than Zhang Jiuling?" Since Zhang Jiuling was originally from Qujiang, Emperor Xuanzong's question quickly was known as the idiom "Qujiang Demeanor", used to describe Zhang Jiuling's profound, upright and selfless character.  

Tang poetry can be very modern too: read the Pipa Tune poem by Bai Ju-yi and listen to these  musical interpretations by Qi Ran and Chen Mi Ren, Leo Luo Yunxi, and  Allen Ren Jialun :


* https://www.youtube.com/watch?v=XFcKbChgRsg   (Pinyin + translation on screen, Qi Ran and Chinese opera singer Chen Mi Ren )

* https://www.youtube.com/watch?v=BJWZVoAd750 (Luo Yunxi on stage with Chinese opera artist Tian MiaoMiao, guqin player Bai Wuxia)

* https://www.youtube.com/watch?v=-HJYUrL6wU4 (Allen Ren Jialun with famous pipa player Fang Jinlong in 2018)

* https://www.youtube.com/watch?v=HTjkZPEPZ5Q (Allen Ren Jialun, new version, 2022 for Hunan TV)

Last episode 40  37:00-37:39  The name change

Master Ren explained that he could not call her Sun Wukong  孙悟空  who is the famous Monkey King. But after having long considered her as an impish but sweet and wild little "Monkey Sun",  he found a name that would be more serious and cultured than 孙头头 : one that would fit a growing leader, and remind also of the greatness of the path-clearer for pilgrim Tang Sanzang in the epic Journey to the West, the most universally known Chinese classic.

Dà Yuàn 大 愿 means "Great Ambition" and being humble does not mean one should lack ambition. The "yuan" key and personal name (usually last in Chinese two-character given names) is that in 意愿 Yìyuàn (will) which is also in 愿意 Yuànyì  (be willing to)  It is also near homonym with some words that are linked to officialdom such as 教员 Jiàoyuán (teacher), 辅导员 Fǔdǎo yuán (counselor). The new name will establish her as one who has the drive and backing of her elders, sect and authorities.

It is a very nice sounding name too, in Chinese, and Da Yuan will sound harmonious with her husband's name Tian Zhen.

Actually there are even more implications perhaps  in the name change, since 孙 is also the family name of the great Sun Zi / Sun Tzu 孫子 pen name of the famous general and author of The Art Of War!