The Knight in the Area

The Knight in the Area (エリアの騎士, Eria no Kishi) also known as Area no Kishi is a manga written by Hiroaki Igano and illustrated by Kaya Tsukiyama.

Plot
Kakeru Aizawa is the younger brother to Suguru Aizawa, a soccer prodigy belonging to Japan's under–15 national team. Prior to the series, Kakeru quits his position as a forward after a traumatic experience prevented him from playing with his left leg and settles for a managerial position. After the two are hit by a truck, Suguru dies and has his heart transplanted into Kakeru. With it, Kakeru returns to football to achieve his brother's dream of winning the World Cup.