Kaiki Nishhoku (a Touhou LW original) refers to a total solar eclipse, a celestial phenomenon where the Sun is fully obscured by the Moon. This is an apt temperament for Seiga, who is good at opening holes in anything. Seiga is endowed with Water Phase, as a necromancer who controls souls and corpses of the dead, and Star Essence, as a wicked hermit who carves out her own fate. The flexible and patient Water Phase resists Metal Phase, because metal collects water, but it is weak to Earth Phase, because earth directs water. The diverse and uncooperative Star Essence resists the cooperative and indecisive Moon Essence, but it is weak to the charming and arrogant Sun Essence.

The ability of Seiga Kaku from a world overflowing with divine spirits (a Touhou LW original). It's basically the same as our Seiga's ability. Seiga Kaku is the person who taught Taoism to Toyosatomimi no Miko. She is a hermit who emigrated from China. However, some whisper that she is a wicked hermit behind her back. Apparently, she decided to cross the sea to Japan because there were plenty of Taoists just as powerful as her in China, the birthplace of Taoism. Considering Seiga's free-spirited nature, she probably didn't flee from China to avoid conflict. It's much more likely that she sought new pastures simply because she was tired of listening to the unfounded accusations against her. She probably seeks to insinuate herself with powerful and talented individuals like Miko because her ambition compels her to always reach for greater heights, like when she abandoned her family to become a hermit. It was also Seiga who advised the troubled Miko to spread the teachings of Buddhism across Japan for political reasons while seeking the truth of the universe with Taoism in secret. The fact she was in a position to advise the regent, albeit unofficially, indicates she was probably a member of the Mibube, an official institution of the Imperial Court that supported the emperor's children. They were in charge of managing the nation's finances that were set aside for the princes and princesses, as well as providing them with tuition and military training. Some even claim that the institution was created solely for the sake of Toyosatomimi no Miko. While nothing is confirmed, Seiga being one of the Mibube's foreign tutors would explain her uniquely privileged position in the Imperial Court. One can easily imagine Seiga attaining this position by exploiting loopholes in the law with her ability. The court at the time was hungry to learn all that they could from China's logical state-of-the-art culture, so with Seiga being an expert on Taoism, she was probably welcomed with open arms. Choushimaro, the groom of Miko's beloved kurokoma of Kai steed, might have also been a member of the Mibube institution. Another member, Ooube no Oo, was responsible for the God of Eternal Night incident that occurred after Toyosatomimi's supposed death. This might have also caused a religious schism within the institution, particularly if the rumors are to be believed that the head of the institution was none other than Hata no Kawakatsu. When youkai devour the flesh of hermits, they become even more powerful. That's why youkai are the enemies of hermits. Byakuren Hijiri has a number of youkai disciples as the head priest of Myouren Temple, so to hermits, that makes her an evil overlord who could potentially create a kingdom of youkai. And to Seiga, she is also a fool who truly believes in the teachings of Buddhism they spread for political reasons and a nuisance who sealed the spirit mausoleum where Miko lies at rest. Seeing as Seiga seems to have made Yoshika, her jiang shi servant, from the corpse of someone who lived during the Heian period (794-1185), it's likely that she continued to live somewhere in Japan while Miko and the others slept in the mausoleum. This shows how earnestly she must've wished for Miko's resurrection. It's unclear whether Hata no Kawakatsu told her about Nestorianism during their time in the Mibube or if she learned about it at another time or by some other means, but Seiga knew about the Western religious concepts of a saint being resurrected coinciding with the advent of a new kingdom and worldwide reformation, as well the story about the son of a god being born in a stable. She probably believed the advent of a new age would be her chance to do what she couldn't do in China and finally achieve her dream of becoming like He Xiangu (her inspiration for becoming a hermit in the first place). That might explain why she's so determined to complete Miko's resurrection, no matter who gets in her way or how long it takes.