Until I can attach appropriate links to everything, please just use this handy website to find out about anything here you haven't heard of before! They're all the basic holidays and festivals that your born-and-raised-in-Japan characters would know about, after all.
1st-5th :: Ideal sakura viewing
5th :: Spring break ends, 1st term begins (Opening ceremony, club fair for recruiting first years, etc.)
29th :: Showa Day, birthday of former Emperor Showa
( Golden Week :: April 29th (Thursday), and then May 1st-5th (Saturday through Wednesday), making for one stand-alone day off and then a 5-day weekend.)
3rd :: Constitution Day, On this day in 1947, the new post war constitution was put into effect.
4th :: Greenery Day, a day to commune with nature, to be thankful for blessings, and to foster an abundant spirit. (was April 27th until 2007, in accordance with government policy)
5th :: Children's Day, Families pray for the health and future success of their sons by hanging up carp streamers and displaying samurai dolls, both symbolizing strength, power and success in life.
11th - 13th :: Mid-term exams
7th :: Tanabata festival
7th-9th :: Final exams
12th :: 1st term ends, report cards distributed, summer break begins
Mid-month :: Bon festival (in the Tokyo area)
19th :: Marine Day (a modern secular holiday that started in 1996 for visiting the ocean; no traditions beyond that, yet)
23rd :: Summer break ends, 2nd term begins
- 20th :: Respect for the Aged Day, honoring senior citizens. Annually, Japanese media take the opportunity to feature the elderly, reporting the population and highlighting the oldest people in the country.
- Late in the month: Students from other semester systems around the world may begin their enrollment.
11th :: Health & Sports Day; As Health and Sports Day is a day to promote sports and physical and mental health, many schools and businesses choose this day to hold their annual undou-kai (運動会), or Sports Meet.
3rd :: Culture Day
23rd :: Labour Thanksgiving Day, celebrates workers and gives thanks to civil servants and blue-collar workers, also part of celebrating the older traditional holiday, niinamesai, an ancient rice festival.
20th :: 2nd term ends, report cards distributed, winter break begins
23rd :: Emperor's Birthday
1st - 3rd :: New Year's celebrations
3rd :: Winter break ends, 3rd term begins
11th :: Coming of Age Day
Early in the month :: National Center Test for University Admissions, taken over a 2-day weekend by students or ronin trying to get into college
3rd :: Setsubun; seasonal division, warding away bad spirits
11th :: National Foundation Day
14th :: Valentines' Day
Early in the month :: Graduation for third years
3rd :: Dolls Festival
14th :: White Day
17th-19th :: Final exams
21st :: Vernal Equinox Day (春分の日), an official national holiday spent visiting family graves and holding family reunions
22nd :: 3rd term ends, report cards distributed, spring break begins
Please reply here with any comments on proposed additions to the calendar, and the mod team will look into it, and possibly ask you for more information!