Shiba didn't know exactly how valuable that sleeveless coat was, but at least, he knew that it was more valuable than all his possessions together.
From the beginning, Shiba hadn't been too picky about clothes.
He had been wearing more formal ones since he became the deputy principal of the academy, but since those clothes were damaged while fighting the golems, he just put on a simple tight sleeveless shirt and nothing else. After all, it was a pain for him to be constantly changing clothes that broke easily, so at least he preferred that was something simple.
Moreover, at his level, clothes were merely aesthetic because the weather couldn't affect him. One would need to use a Law Skill to make him feel cold or hot, and ordinary clothes would be useless in that situation.
Thus, he didn't mind too much how the sleeveless coat would look on him and just put it on his body.