Generally, Japanese culture tends to handle emotional expression a little less directly than in English-speaking countries, especially where romance is concerned. In particular, couples in Japan aren’t nearly as likely to regularly say “I love you” as their Western counterparts are or be seen smooching in public.
In certain situations, though, these roles get flipped. For example, while most Westerners would feel awkward making the explicit statement, “Please be my boyfriend/girlfriend,” in Japan that exact phrase, tsukiatte kudasai, is a pretty common romantic milestone, and something that many actually expect their partner to say in order to explicitly recognize the nature of the relationship.
Now, couples can even have their affection officially recognized, as lovers in Japan can submit government documents certifying their love for each other.