The reisen was originally a gift money presented from Shugo Daimyo (Japanese territorial lord as provincial constable), temples and shrines in celebrations such as the appointment of Seii Taishogun (literally, "great general who subdues the barbarians") at the Muromachi bakufu (Japanese feudal government headed by a shogun). The word 'reimotsu' was used when non-cash gifts were presented. The reisen was later called the ikkonryo to indicate the gifts (money or goods) presented to the Muromachi bakufu, the Imperial Court, Shugo Daimyo, and the government officials working for them in exchange for receiving a government post or a favorable ruling in a lawsuit.
In a state before the modern era, rights did not belong to the people, but they were types of favors given to those in power such as a state for their distinguished services. As a result, everyone from Daimyo (Japanese feudal lord) to commoners thought it a natural courtesy and righteous judgment to present something beneficial such as money or goods in return when he/she was given a right by the higher authority. In short, it is necessary to bear in mind that the line between the reisen and bribery was subtle and ambiguous in the legal concepts before the modern era.
This kind of custom had existed since ancient times, and then, in the Kamakura period, a party to a suit often invited those in charge of the case to a drinking party to receive a favorable sentence. The another name of later 'ikkenryo' is said to have originated from this custom.
In the Muromachi and Sengoku (warring states) periods, the Imperial Court and the Muromachi bakufu were in severe financial difficulties, and as a result, the reisen as a gratuity was expected to be presented as a condition for receiving the documents of awarding government posts and official positions as well as of the tsugime ando (receiving again the ando-jo, or document to authorize the ownership and control of the shoryo, or territory, in case of appointment of Shogun); before long, the logic was changed, and whether the documents were issued or not came to depend on the amount of the reisen presented.
When the financial conditions of the Imperial Court and the bakufu greatly worsened, to present the reisen was required for those who asked for various kinds of privileged rights such as: tax exemption including the tansen (a kind of provisional tax in medieval Japan) and the hanzei (tax system in which the Muromachi bakufu allowed Shugo, or military governors, to collect half of the taxes from manors and demesnes as military fund); issuance of the kinsei seisatsu (notice of banning orders on a street bulletin board); ban on the construction or abolition of a sekisho (checking station); granting of commercial privileges such as the za (privileged guild); or support for a lawsuit. At the same time, those asking for privileged rights willingly offered the reisen, expecting to receive favorable treatment. This trend was established in the whole society among Shugo daimyo, lords of the manor, leaders of the soson (a community consisting of peasants' self-governing associations), prominent merchants such as the doso (pawnbrokers and moneylenders), and even commoners. The targets for the reisen also widely ranged from Shugo daimyo ruling the ryoseikoku (province), the Imperial Court, the bakufu, powerful figures having influence over Shugo (provincial constable), Court nobles, Shugodai (deputy of Shugo), even to government officials in charge of actual administrative and legal practices such as the bugyoshu (group of magistrates). The reisen is said to have been a major source of income especially for Court nobles and the bugyoshu (group of magistrates) with financial hardships to sustain their lives.
In the legal procedures, in particular, at that time, a party to a suit requested a hearing on certain dates and the person in charge of the case such as a magistrate decided on whether to approve the dates; thus, the lawsuit was likely to stop for years if he rejected the request. This caused one to offer the reisen just to start a lawsuit before presenting the reisen to receive a favorable ruling. The reisen and ikkenryo were openly booked as expenses for lawsuits on the financial records at that time, and also there is a record that in the lawsuit arising from a dispute between villages, the lord of the manor where the village belonged to paid the reisen and ikkenryo for the village and charged them later.
The Imperial Court and the Muromachi bakufu issued an order to prohibit those in charge of cases from accepting the reisen, but it had no effect since the Imperial Court and the bakufu themselves received large sum of reisen. Since the Onin War, furthermore, Court nobles and the bugyoshu, whose shoryo in rural area were usurped by Daimyo in the Sengoku period and the kokujin (local samurai), lost their income and were too poor to sustain their lives without the income of the reisen, making it difficult to even issue a ban on the reisen. It was not until the establishment of the Edo bakufu, which formed a unified government and was engaged in creating a sound financial footing and the samurai code, that the reisen was considered to be a bribe and strictly prohibited.
In the Edo bakufu, however, the 'sokushu' (initiation fees) that Koke (government position in charge of rituals and ceremonies) received from Daimyo when teaching manners can be considered to be a type of reisen officially recognized by the bakufu; in fact, it is possible to assume that the fight between Naganori ASANO and Yoshihisa KIRA in the first scene of the "Chusingura" (The treasury of Loyal Retainers) was over the nature of the 'sokushu.'
It is also possible to suppose that the issues of bribery and corruption kept appearing from the Edo bakufu through and after the Meiji government because people had been accustomed to the concept of the reisen and not felt so guilty for a long time.
The reisen and ikkenryo were, by their very nature, called according to different names.
The following were the major ones: 'toritugi-sen,' 'han-sen,' 'seisatsu-sen,' 'origami-sen,' 'hikei,' 'shuko-ryo,' and 'ikkon-sen.'