What is "Yukyu"（有給）?
"Yukyu"（有給）in Japanese means 100% paid day off.
給 means "salary" and 有 means "eligible". So it means vacation which is still eligible to get salary.
Even if you take a day off, your salary will NOT be reduced on that day. In Japan, employees are entitled to take "Yukyu" （有給）under the Labor Standards Law.
Paid day off: If they have been working for more than half a year since they were hired and have worked more than 80% of all working days, the number of days granted is 10 days.
Especially in recent years, Japan legally requires employees to take at least five days of paid leave per year. Employers will be punished if employees do not take leave. Employers will also want their employees to spend their vacation.
Need to give notice to supervisor before taking Yukyu
It is your right to take a day off but you need to give notice and get approval from your supervisor beforehand.
Do not worry !
In most cases, applying for a vacation is unlikely to be rejected by your supervisor in Japan.
In other words, the rules for granting vacations do not allow your boss to refuse to take vacations without very reasonable reason(時季変更権）.
To reject your application for vacation, very reasonable reason such as "interference of normal operation of the business" （事業の正常な運営）is needed.
The factors that are judged to "interference of normal operation of the business" are as follows.
-Business scale and business content itself時季変更権とは？行使するための条件や注意点を徹底解説 | jinjerBlog (hcm-jinjer.com)
-Job description and job characteristics of employees who applied for paid leave
-Difficulty in allocating alternative personnel
-Many employees take a day of on same season
How many Yukyu can I take?
The rate of paid leave taken by workers in Japan has been 45-50% since 60% in 2015, but in 2021, it was taken 12 days out of 20 days of paid leave, and it became 60% again. Anyway, Japanese government pushed companies for employee to take Yukyu more. Moreover, it is right to take all Yukyu days in Japan.
Do not worry and take a vacation in Japan!