Gunchujo were documents that proved participation in battles and other military exploits in medieval Japan.
The relationship between lord and vassal in medieval Japan was based on favor and service. When vassals participated in military action initiated by their lord with their own soldiers or showed their military exploits on the battlefield (contributing service), the lords were in return required to recognize 'participation' and 'military exploits' of the vassals not for their own private battle or war but for a legitimate 'official battle' in order that they be granted favor and compensated for their service, or receive new territory as a reward (the granting of favor and compensation for service).
Therefore participation in war or military exploits had to be proven for later rewards. For this reason such documents began to be issued under the name of the lord.
Such documents were written according to the following format; the vassal's name came first and then details regarding the facts of the vassal's superior military valor were stated (often with the words: 'I report our superior military valor.')
Next came further details about the war or battle in which the vassal served, what damage was afflicted on the enemy, and what damage its own forces suffered. It also listed the busho (Japanese military commanders) with whom the vassal fought on the battlefield, in order to prove his superior military valor (the name of busho were sometimes not listed). At the end the words 'I would like my superior military valor to be recognized as evidence for future (rewards)' were written, although the wording differs slightly from document to document.
The document ended with the words: 'I hope that this will be granted.'
In many cases, it was addressed 'To obugyosho (an expression of respect relating to a magistrate's office).'
When the Gunchujo was submitted to the administrator of the troops and certified to be true, the document took effect with the addition of the approval mark of the administrator (Kao [written seal mark]) at the end of the document (or the head in some cases) and with words along the lines of 'I looked through the above and agree that it does not differ from the facts.'
It appears that some lords may have prepared and issued similar documents themselves.