Template:Lunr-calendar
C/1FE/1F391-16
Renders a negahex date from Lunarian. The first three unnamed arguments are the month, day, and year in decimal; you can also include an explicit year argument that replaces the final slash and the third number. For example, the page Tifa Kerʉnka uses this template with no third argument (defaulting it to the equivalent year to 2026, 1F391-16) and with the year argument set to "/?". This can also be used to entirely remove the year, by setting year to an empty string.
To be perfectly clear, this is not actually based on Template:Base, but reimplements it; this is partially because that allows for the final subscript -16 to go after the entire date, and partially because Base gives the decimal number formatting even if format is set to false.