what did osman i regard the byzantines as?

Osman I regarded the Byzantines as his principal rivals and enemies on the frontier, especially as the main obstacle to his expansion in northwestern Anatolia. His campaigns were directed against Byzantine-held territory, and the conflict became a defining part of the early Ottoman rise.

In context

• He saw them less as abstract “foreigners” and more as the power controlling nearby lands he wanted to take.
• In practice, that meant steady warfare, raids, and the capture of Byzantine fortresses.

• The frontier struggle with Byzantium helped shape the early Ottoman state.

Simple answer

So, in short: Osman I regarded the Byzantines as military opponents and territorial rivals.