According to tradition, the Tokugawa forces were in opposition to the royal family and this is seen in Tokugawa’s refusal to accept the royal clan’s mon or crest, but favouring his own clan’s.
According to Mark W. MacWilliams (Pilgrimages — Canton to Chichibu), the Tokugawa crest …
The legend goes that Emperor Go-Yōzei presented a new imperial crest (presumably a design based on the imperial Chrysanthemum emblem above) of the Minamoto clan, to the Tokugawa founder, but Ieyasu declined the new symbol. Instead, he favored the old crest(below which is an inverted variation of the Matsudaira crest), thereby showing the bearer’s allegiance to the shogunate. In this way, he showed support for the shogunate as opposed to the monarchists, whose cause is symbolized by the Imperial throne’s chrysanthemum crest as seen at the Imperial Palace (“Japanese Family Crest”).”
Matsudaira clan (松平氏 Matsudaira-shi) was a Japanese samurai clan that claimed descent from the Minamoto clan. It first originated in and took its name from Matsudaira village, in Mikawa Province (modern-day Aichi Prefecture). Over the course of its history, the clan produced many branches, most of which also centered on Mikawa Province.
In the 16th century, the main Matsudaira line experienced a meteoric rise to success during the headship of Matsudaira Motoyasu, who changed his name to Tokugawa Ieyasu and became the first Tokugawa shogun. Ieyasu’s line formed what became the Tokugawa clan; however, the branches retained the Matsudaira surname. Other branches were formed in the decades after Ieyasu, which bore the Matsudaira surname. Some of those branches were also of daimyo status. See Tokugawa Ieyasu, the former Matsudaira Motoyasu depicted below along with the crest.
The crest is believed to stem from a mythical clan, the Kamo clan, which according to legend, descended from Yatagarasu, a Matsudaira village in the Higashikamo District of Japan. The Aoi hollyhock is the emblem celebrated in the Aoi Festival held by the two Kamo shrines, a festival dating back to the 7th c. (p. 34, Japan Encyclopedia) – Kamigamo-jinja and the Shimogamo-jinja every May 15, which is an agricultural festival to pray for an abundant harvest and protection against disaster. The Kamo shrines enshrine the Wakeikazuchi no Kami, son of Tamayori-hime and brother of the legendary first Emperor Jimmu Tenno.
Predating Kyoto‘s establishment as the national capital in 794, the Aoi Matsuri began in the 7th century. There were natural disasters occurring that were believed to be caused by the deities of the Kamo Shrines. After the Emperor made offerings to the gods, the disasters subsided and a tradition was begun. The Aoi hollyhock is believed to ward off thunderstorms and earthquakes (see Aoi Matsuri Hollyhock Festival). The two Kamo shrines are thus regarded as the protector shrines of the Imperial Palace and capital (source: p. 201 Handbook to Life in Medieval and Early Modern Japan by William E. Deal).
Kamo-jinja priests in Kyoto used the Aoi flower motif as insignia for the shrine. Although Ieyasu Tokugawa never used the surname Matsudaira before 1566, his appointment as shogun was contingent on his claim to Matsudaira kinship and a link to the Seiwa Genji (who were the most successful and powerful line of the Japanese Minamoto clan that were descended from Emperor Seiwa). However, some members of the Tokugawa family were known devotee worshippers at the Kamo-jinja shrine. The Tokugawa family used the Aoi as their insignia, and families not related to the Tokugawa were forbidden the use of the insignia (source: Japan Encyclopedia by Louis-Frédéric). This led to a belief that the Tokugawa may have actually descended from the Kamo clan, (賀茂氏 Kamo-shi) which is a Japanese sacerdotal kin group thought to have had roots in the Yayoi period. The clan rose to prominence during the Asuka and Heian periods when the Kamo are identified with the 7th-century founding of the Kamo Shrine.
During the Aoi Matsuri festival, some 500 people wearing splendid ancient costumes and traditional make-up parade through the main streets of Kyoto. The extravagant parade is in the style of the ancient Heian Court. Everything in the parade is adorned with the hollyhock leaf crest, also called “aoi” … aoi leaves are used as ornaments not only on the people’s costumes, but even on cows and horses, so this festival came to be called Aoi Matsuri.
Source: Buddhika Weerasinghe/Getty Images AsiaPac
The festival re-enacts the procession of officials delivering the Emperor’s message and offerings to the two shrines of Shimogamo and Kamigamo. The most important position held in the parade is the messenger on horseback wearing a gold sword at his side, who is followed by a train of attendants. The highlight of the procession is the parade of women accompanying the proxy of the imperial princess serving the deities.
Mark W. MacWilliams’ Pilgrimages to Bosatsu-East and West; Imperial Family and Nationalistic Pride
Otomo clan – The Kamo clan is also closely related to the Otomo clan who helped establish the Ashikaga shogunate (source: Ôtomo-no-Sakanoue-no-Iratsume’s Visit to the Kamo Shrine)