Just what it says on the label - a fictional marriage certificate for fictional characters. It originated as a meme on pixiv, likely as one of their many exercises in creativity.

All tagged entries involve the use of a template:
* Pictures of the groom (left) and bride (right)
* Names of the groom (left) and bride (right), including both kanji reading and pronunciations where possible
* Date of Birth of groom (left) and bride (right)
* A brief description of how the couple first met
* Occupation of groom (left) and bride (right)
* Miscellaneous other comments from the couple and/or any witnesses (friends, family, enemies, etc.)
* Signature and hanko stamp of husband (left) and wife (right). Also acceptable are fingerprints, personal logos, bloodstains, etc. A simple signature is fine if nothing else will do.

h4. See also
* [[Marriage certificate (object)]], when a marriage certificate appears as an object in an image.
pixiv婚姻届