Shinjin (真人) is the ideal of human in the thought of Laozi and Zhuangzi and Taoism. It is sometimes used as another name of sennin (hermit).
Mahito (真人) is one of the kabane (hereditary titles) enacted by Yakusa no Kabane (the eight honorary titles). Details are explained in this article.
Mahito was one of the Yakusa no Kabane established in 684 and was top grade kabane. It is said that 'Mahito' meant the nobilities or that it is the literal translation of the caste system of Silla. Basically, it is given to close blood relatives of Emperor Keitai and the descendants of the subsequent emperors and princes. There is a theory that the title of tenno (天皇) (emperor) derived from Tien-Huang-ta-ti (天皇大帝) of Taoism, and also some say that this 'Mahito' also came from Taoism. In Yakusa no Kabane, michinoshi is also derived from a term of Taoism. Also Emperor Tenmu's okurina (a posthumous name) 'Oki no Mahito' means high rank hermit who lived in the holy mountain in the sea called 'Eishu' according to Taoism.
Bestowing the kabane of Mahito was a part of the pro-Imperial Family politics which was the concept of Emperor Tenmu. According to an article appeared in November 684 in the "Nihonshoki" (Chronicles of Japan), 'Following 13 clans should be given the kabane of Mahito; Moriyama no Kimi, Michi no Kimi, Takahashi no Kimi, the Mikuni clan, Taima clan, Umara no Kimi, Tajihi no Kimi, Ina no Kimi, Sakata no Kimi, Hata no Kimi, Okinaga no Kimi, Sakahito no Kimi, Yamaji no Kimi' and these Kimi kabane clans are probably the descendants of Emperor Ojin and those from Emperor Keitai to Emperor Yomei. After the Emperor Yomei era, descendants of emperors and princes were often given kabane in the Nara period and the number of Mahito amounted to more than 48 clans which are recorded in the "Shinsen Shojiroku" (Newly Compiled Register of Clan Names and Titles of Nobility) (If it includes those which appeared in "Rikkokushi" [the Six National Histories], the number of Mahito clans increases). However, since it was the in the middle of expansion of power by Fujiwara clan, the definition that "Mahito = noble" was beginning to collapse, and there also appeared a case when Mahito was bestowed as a punishment such as HIKAMI no Shioyaki and Imperial Princess Fuwa. This trend strengthened in the Heian period and when YOSHIMINE no Yasuyo (the prince of Emperor Kanmu) was given the kabane of YOSHIMINE no Ason in 802, the number of people who were from the Imperial Family or had the kabane of Mahito increased who wanted to be given the kabane of Ason. Mahito clans who lost political value gradually disappeared from the political world.