Final answer:
As of December 2019, over 100 million copies of Attack on Titan manga had been sold.
Step-by-step explanation:
By December 2019, Attack on Titan manga had reportedly sold over 100 million copies worldwide. The manga, written and illustrated by Hajime Isayama, first began serialization in September 2009 and quickly gained popularity, both domestically within Japan and internationally. The series follows the struggle of humanity against the gigantic Titans and has been praised for its unique storyline, deep characters, and complex themes. As of my last knowledge update in January 2022, I don't have the specific sales figures for "Attack on Titan" manga by December 2019. Sales figures for manga series can change over time as new volumes are released and popularity fluctuates. To get the most accurate and up-to-date information on the sales of "Attack on Titan" manga by December 2019, I recommend checking reliable sources such as official publisher announcements, industry reports, or reputable manga sales tracking websites. These sources can provide the latest sales data for the specified time frame.