The 17-year-old broke into the BVB first-team squad in the second half of the 2019-20 season and made 18 appearances in all competitions, scoring once.
Reyna is now looking to kick on again in the coming campaign, once more starring alongside fellow youngsters Sancho and Haaland, who have each turned 20 this year.
Sancho has been widely linked with a move to Manchester United, yet Reyna, while discussing his own future, insists Dortmund are no stepping stone.
"I'm very, very happy here right now," the English-born United States youth international told Bild. "That is all that counts.
"Dortmund is not a bus stop. This is a club that is fighting for titles. The incredible fans alone make BVB something special."
Reyna's Champions League debut saw him assist Haaland for a winning goal at home to Paris Saint-Germain, an experience the teenager still reflects fondly on despite Dortmund's aggregate defeat.
"With Jadon and Erling, it is really fun to whirl around on the pitch," he said. "In the Champions League game against Paris, we created the storm and won 2-1.
"Two [then] 19-year-olds and a 17-year-old - that was pretty cool. The club can be proud of that, because it is exactly what it stands for."