Both are derived from Greek. But Latin diverged earlier. This is why their B reads like B as in Classical Greek, whereas in cyrillic and in Modern Greek B reads as V.

Some letters are completely unrelated. The English W is a double V whereas the cyrillic Ш is a "sh", just as the ש in Hebrew. Cyrillic Я is an ι fused with an α and not an inversed R. There was no R in Byzantian Greek. There was rho and it looked like this: P.

Now: how did the latins end up with pronuncing it as π? And why is their eta an h? That's something we should ask a Latinist.