[msla]

https://en.wikipedia.org/wiki/Capital_%E1%BA%9E

That letter, the capital eszett, has existed in German typefaces since at least 1905:

> Historical typefaces offering a capitalized eszett mostly date to the time between 1905 and 1930. The first known typefaces to include capital eszett were produced by the Schelter & Giesecke foundry in Leipzig, in 1905/06. Schelter & Giesecke at the time widely advocated the use of this type, but its use remained very limited.

Eszett is usually just a lower-case form; it is most often upper-cased to SS, or two capital letter esses, being an example of how changing case does not always preserve the number of letters in a text. Capital eszett is very rare, but it was in uncommon usage in German text, and so it was added to Unicode.