The music crew utilizes Kokyū (or Erhu maybe) when it comes to a lyric scene, which is very expressive.
The authoress of the original manga attended a Buddhist high school (as a Chinese I thought there were only Catholic high schools,lol) and got this spark of inspiration from the Buddhist version of the heaven, which is, according to the scriptures, decorated with gems. So she wondered where the gems come from, And there it goes, the gem-hunt by the moon-people.
The setting might be a little bepuzzling to viewers without a relevant cultural background, so I'll just list a few concepts that might shed some light on it.
Shintoism. Japanese pagan religion, basically believes that everything has a spirit.
Vajra. The namesake of Kongo Sensei. Means diamond/thunderbolt. Kongo is a loanword from Chinese, 金剛, lit.metal+adamant. The corresponding scripture is called "Diamond Sutra", which is , according to Wikipedia, a part of the " 'Perfection of Wisdom' genre, and emphasizes the practice of non-abiding and non-attachment. The Diamond Sutra is one of the most influential Mahayana sutras in East Asia, and is a key object of devotion and study in Zen Buddhism."
Apsara. The most probable graphic archetype of the moon-people soldiers. You can google image "apsara Dunhuang" to see them. Wikipedia again:"a female spirit of the clouds and waters""In Indian mythology, apsaras are beautiful, supernatural female beings. They are youthful and elegant, and superb in the art of dancing. They are often wives of the Gandharvas, the court musicians of Indra. They dance to the music made by the Gandharvas, usually in the palaces of the gods, entertain and sometimes seduce gods and men."
Preta. Possible spiritual archetype of the moon-people soldiers. Hungry ghosts. Wikipedia:"Pretas are believed to have been false, corrupted, compulsive, deceitful, jealous or greedy people in a previous life. As a result of their karma, they are afflicted with an insatiable hunger for a particular substance or object. "
Karma. Cause and effect. Again wikipedia:"action, work or deed; it also refers to the spiritual principle of cause and effect where intent and actions of an individual (cause) influence the future of that individual (effect). Good intent and good deed contribute to good karma and future happiness, while bad intent and bad deed contribute to bad karma and future suffering."
Taṇhā. Greed, craving, source of Dukkha, which means suffering in Bhuddhism.
Whew, that was monolithic.
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edit: apparently the imagery of phos being forged into an alloy of multiple substances also has an allusion to it.
Seven treasure of buddhism, are gold, silver, lapis lazuli, ruby, crystal, coral and emerald, which may be associated with the Seven Factors of Enlightenment.
