Naofumi Iwatani from The Rising of the Shield Hero isn't the luckiest of main characters in the isekai genre. Not only did he receive a piece of non-offensive equipment, his first companion, Princess Malty, also betrayed him in the nastiest way possible, turning him into a distrustful antihero. He did find loyal subordinates in Raphtalia and Filo, who never abandoned him no matter the situation. But before the two joined his party, there was already one person who believed in Naofumi despite the sea of lies.
Even though Malty was a hateful character, her shrewdness is commendable. She managed to perfectly play Naofumi, successfully destroying him and his reputation. Naofumi was forced to survive alone without any item, information, or companion. But while the entire kingdom scorned him, the town's weapon shop owner was the only one who believed in him.
When Erhard heard of the news, he believed the accusations against Naofumi. However, his views changed after meeting the Shield Hero and seeing his reaction. Convinced that allegations against Naofumi were dodgy at best, Erhard sold him a green cape. He told the hero that he would put the five copper coins on his tab, which Naofumi stealthily paid later on. Since then, Erhard welcomed Naofumi without any question or judgment. He sold him the equipment he needed and also gave him any information he knew.
The moment Naofumi got the demi-human Raphtalia, the first loyal member of his party, he brought her to Erhard. At this point, Naofumi had to threaten the other merchants just to do fair business with him. Erhard, however, continued to treat the accused hero like any other customer without any unnecessary demand. The same was true when Filo joined the gang, though the little girl managed to trick Erhard off a good sandwich. Naofumi's relationship with Erhard became good enough that the Shield Hero often used his shop as a meeting place of sorts. Even though the weapon shop owner frequently whined, he was pretty gung ho about it.
During Malty and Aultcray's trial, Erhard was convinced that it would be a good show. He expected Naofumi's name to finally be cleared and was rather elated when it happened. He was quick to congratulate Naofumi when the hero came to his shop, and he proved his closeness to him when he grudgingly let him copy his entire shield inventory.
Raphtalia, Filo, and Melty have repeatedly proven their allegiance to the titular Shield Hero, but that does not necessarily mean they were the only ones who were on the hero's side. Although it can be argued that Erhard has his initial doubts, he has constantly supported Naofumi in any way he can from his lowest point to his greatest achievements. It is highly likely safe to assume that their good terms will carry over on the second season of The Rising of the Shield Hero.