The Gaon Chart is the national chart of South Korea and is intended to be the equivalent of Oricon in Japan and Billboard in the United States.
The Gaon Album Chart are a set national charts that ranks the best-selling albums, including mini-albums and singles, in South Korea, provided by the Korea Music Content Industry Association. The charts are made up of charts tracking domestic album sales, international album sales and a combined overall album sales in weekly, monthly and year-end format.
XIA Junsu’s ‘How Can I Love You’, for ‘Descendants of the Sun’ OST Part 10, was released on 2016.04.14 and has ranked 1st on Gaon Weekly Digital Chart.
Source: Gaon Chart
Shared by: JYJ3
JYJ3 
Congratulations Xia Junsu!!!!
#kimjunsufighting
#How_Can_I_Love_You
since it came out, and still get no.1 go Xia, rock the industry baby, mmm wanna bite his cheeks.