Japanese tea has three major components: catechin (astringent ingredients), L-Theanine (umami ingredients) and caffeine (bitter ingredients).
Unlike others, caffeine is often regarded as a “nuisance”. Japanese also care about caffeine, but, if anything, relatively lenient to it in general. Sometimes, it is favorably received when people want to feel refreshed and keep themselves awake.
Why don’t Japanese worry that much about caffeine? There seem to be mainly two reasons.
First, it’s because of “a tolerance to caffeine”. Japanese have high tolerance to caffeine while Europeans and Americans have low tolerance. (Japanese have low for alcohol, though.)
Second, it’s thanks to “L-Theanine”. A report says the component suppresses the action of caffeine to some extent. Therefore, caffeine in tea doesn’t have a great impact on us as much as it is supposed to do.
L-Theanine is extracted with lower-temperature hot water, while caffeine is extracted with higher-temperature hot water. Considering this, in terms of both taste and benefits, it is reasonable to infuse Gyokuro and high-quality Sencha, both of which have more caffeine, in lower-temperature hot water. More L-Theanine could help moderate the act of caffeine. 
