Eyeshield 21 is a coming-of-age sports manga written by Riichirou Inagaki and illustrated by Yuusuke Murata. It ran in Weekly Shounen Jump from 2002 until 2009, and its 333 chapters were collected into 37 volumes.

The story centers on Sena Kobayakawa, a short, wimpy first-year student at Deimon High School who spent most of his childhood running away from and gofering for bullies. Thanks to this, Sena developed superhuman speed and agility, a talent that Deimon High's maniacal shadow tyrant, Youichi Hiruma, quickly discovered. So Hiruma forcibly drafts Sena into his struggling American football team, the Deimon Devil Bats, as their new running back. He also makes Sena wear a tinted visor and use the codename "Eyeshield 21," so that other sports clubs don't recruit him.

Throughout the series, Sena gains new teammates as they overcome numerous obstacles in the tough world of American football, all with their eyes on Japan's high school national championship, the Christmas Bowl. As he faces down new rivals and difficult plays with each new game, he grows into a braver person and a stronger athlete who learns to love the sport.

Seijuurou Shin of the Oujou White Knights is Sena's first-ever rival, and one of the reasons he decides to keep playing American football. Sena is also the first player to ever outrun Shin, which earns him Shin's respect early on, both as a fellow athlete and a worthy opponent. Even as Sena meets and plays against other rivals, Shin is the one he looks up to the most, and that admiration is mutual. Through the duration of the series, their rivalry is one of the main reasons they both seen to improve their abilities, all with the shared hope of one day facing off again on the gridiron.

Although I read the first half of Eyeshield 21 back in 2015, I got very attached to their relationship once I started re-reading it in early 2021. Size and body-type differences are a charm point for me, and ShinSena is a stellar example of this: Shin is a tall, muscular stoic, while Sena is a short, dainty, recovering scaredy-cat. I find that contrast SUPER cute! Plus, despite all of this, they have a shared passion for self-improvement, looking to one another as both inspiration and motivation to become better athletes. They both also have weak social skills, which make their interactions in-story quite amusing (though Sena seems to fare slightly better in this area).

I've been endeared to these differences and similarities, to the point that I couldn't help but view Shin and Sena's mutual respect as a growing love between two guys on the cusp of adulthood. Shonen sports manga are fertile ground for these sorts of interpretations, as one could see from their large BL shipper fanbases! This chemistry is what holds their rivalry together, and makes theirs one of the more emotionally compelling relationships in the series. Although they are far from each other's only rival, they propel each other forward to surpass their own limits.