Combining Cyrillic Big Yus

It is Big Yus written above another letter. The standalone Big Yus appears in early Cyrillic and Glagolitic writing as a sign for a Slavic nasal vowel. This combining form belongs to the titlo tradition, which placed letters above the line in abbreviated Church Slavonic writing.

Read ⷾ with its base letter and the surrounding historical text. It is a spelling mark for historical Slavonic writing, not a modern Cyrillic letter with a sound of its own.

why does big yus render above a letter?

It follows the base letter in text but displays above it. Type the Cyrillic base first, then ⷾ. The mark on its own cannot show the placement it gets from that base.

In the wider titlo system, combining letters can sit side by side or join above one base. Fonts position or compose these marks, so a general-purpose font may omit one or place it badly; a Church Slavonic font such as Ponomar may handle it better.