Listed below are some recommended websites for planning your future trips.
Flights & Transport
NOTE: Always browse flight and accommodation prices in incognito/private browsing mode
Google Flights Is a flight comparison site. One of the best features allows you to few flight price trends between days. Skyscanner Is another flight comparison site that allows you to compare flight prices.
Information in English on Japan
JET-Setters The JET facebook group for travel. While it is a great place to ask travel related questions, the group isn't a substitute for your own research.