Tanabata, also known as Japanese Star Festival, is a traditional festival celebrated on July 7th (lunisolar calendar) which originated from the Chinese QiXi festival. There is a Tanabata legend that Hikoboshi(Altair) and Orihime(Vega) are only allowed to meet once a year on this day with the help of the bridge of magpies.
Though the sourse is the same story, there are many diffrents between Chinese QiXi and Japanese Tanabata. In Japan, people will decorate a bamboo branch with paper with wishes written on it in Tanabata, it is said doing that your wish will come true. And in China, QiXi is a festival all about couples, it also called "Chinese Valentine's day".