Note: The in-person event is canceled for 2020; however, there is an online event called Air Comiket from December 30–31, 2020.
The winter edition of Comiket (there’s another in the summer), one of Japan’s biggest comic-related events will be happening at Tokyo Big Sight. Admission is free but organisers recommend that you buy the event catalogue. The focus of the event is ‘dojinshi’ – independently created and published manga, so given the thousands of amateur and professional manga artists in Japan, there will be an incredibly wide range of genres and styles on display.
If you’re bringing a costume, be aware you have to pay to cosplay – about ¥800. Also, organisers advise that attendees should be ‘in good health when visiting Comiket and make sure to dress accordingly’. So yeah… do that. The closest stations are Kokusai-Tenjijo-Seimon Station on the Yurikamome Line and Kokusai-Tenjijo Station on the JR Rinkai Line.