In the One Punch Man universe, most characters are unaware of the true extent of Saitama's strength. Saitama's immense power is a running gag in the series, as he defeats all opponents with a single punch regardless of their strength. While a few characters have witnessed his abilities first-hand, they often struggle to comprehend or accept his true power. As for Sonic characters, it is important to note that the Sonic the Hedgehog franchise is separate from the One Punch Man universe. Therefore, the Sonic characters would have no direct knowledge of Saitama's strength unless they exist in a crossover storyline or are aware of his reputation through their own fanbase. If Sonic characters were to react to Saitama, their responses could differ based on the context of the meeting. Some characters, particularly those with a similar focus on speed and strength, may find his power intriguing or try to challenge him. Others might dismiss his power, seeing it as a mere exaggeration or an opportunity for comedic situations, similar to how many characters react within the One Punch Man story. Ultimately, their individual reactions would largely depend on the writing and storytelling decisions made if a crossover were to occur.