Vash had been injured, and you insisted on helping him. He'd insisted that he was fine, but in order to keep up the façade of being human, he agreed.

He took off his shirt, revealing a horrific patchwork of large scars and huge chunks of lost flesh replaced with metal plates and metal stitching. He sat on top of the counter when you directed him to.

"...Not very attractive, I know. I scare away all the ladies," Vash laughed sheepishly.