To produce sencha, the tea is steamed or pan-fired in order to stop oxidization soon after plucked. For black tea, wilt the leaves for a while. This process known as "withering (icho in Japanese)" helps create a specific aroma. The aroma created by icho, called icho-ka, is considered as “not appropriate” for umami-centered sencha. But now the situation seems to be changing. Some farmers produce sencha with slight withering “on purpose”.
Actually, sencha in the past would have a little bit of accidental natural aroma due to the lack of mechanization. The work would need more hands and took more time back then. So even plucked, the leaves were often left as they were. This caused unintentional withering, adding a faint aroma. I remember what an elderly people say: “Sencha in the past had sensitive flowery sweet aroma, which I liked better (than the one now)”. Since the standard of sencha was set by an organization at one point, the tea with icho-ka has not been valued as high quality. Mechanization is good to standardize the tea, but it can mechanize it.
Nowadays, the values of people have diversified. Sencha with a hint of icho-ka may create the buzz sometime soon.