Name this syllable...

A reader recently sent in this image:

I'm a reiki master and found that the origins of the reiki symbols come from sanskrit. I managed to discover the correspondent syllables from two symbols but can't find for one of them. Can I please ask your assistance for that, please? Could you give me the name and the letter for that symbol?

The syllable is vai written in Chinese brush style Siddhaṃ. In Reiki it apparently symbolises 'light'. This is presumably because it is related to the seed syllable of Vairocana - "the illuminator".