Senyu (戦勇。, Senyū) is a Japanese web manga series written and illustrated by Robinson Haruhara [ja]. It started publishing in Nico Nico Seiga website in August 2010; five parts have been released, in addition to a parallel series titled Senyu+. A print version was published in Shueisha's shōnen manga magazine Jump Square from May 2012 to April 2013, with its chapters collected in two tankōbon. Another series, titled Senyu: Main Quest, was published in two parts in Kodansha's Suiyōbi no Sirius online manga section of Nico Nico Seiga from August 2013 to March 2017, with the overall series collected in nine tankōbon volumes.

A 26-episode anime television series was broadcast for two seasons in 2013.

A millennium ago, the Demon King wreaked havoc in the human realm, but was sealed by the legendary Hero Creasion. Closer to the story's present, a large hole appeared in the world, from which a large number of demons emerged. The King has ordered the 75 probable descendants of the original hero to destroy the demons and save the world. The story follows Alba, hero number 45, and his quest to save the world. Along the way, he is accompanied by Royal Soldier Ross, whose somewhat sadistic, antagonistic antics serve as comic relief. Alba quickly teams up with the demon queen herself, who is soon revealed to be a naive, young pink-haired girl who accidentally instigated the demon crisis while making popcorn.

The series starts almost exclusively comedic, with episodic gags mainly involving Alba's bad luck and Ross's abuses. A more serialized story develops halfway into the first part, as an order of twelve powerful demons themed after the twelve months of the Gregorian Calendar starts attempting to revive the original Demon King. Simultaneously, other probable hero descendants also interfere, with lesser demons and government officials caught in the crossfire.

The world's past and Creasion's origins are explored in the second part, culminating in the supposed defeat of the story's main antagonist, the first Demon King. The third part focuses on the remnants of the twelve demons, especially the strange machinations of one of them, Elf November. The fourth volume explores Elf's past and his complex involvement with existence, concluding Senyu's main storyline.

The fifth part serves as an epilogue, elaborating upon the original story and later shifting to a comedic slice of life where the characters adapt to the world after the chaos wrought by the catastrophic events explained in previous parts. The later portion of the fifth part explores some aspects of Elf's past and introduces a new group of antagonists.

Written and illustrated by Robinson Haruhara [ja], Senyu started on Nico Nico Seiga website on August 27, 2010. The first part finished on June 17, 2011, and a second part was published from July 1 of that same year, to February 22, 2013. A third part was published from March 1, 2013, to July 4, 2014. A fourth part was published from August 22, 2014, to February 27, 2015. A parallel story, titled Senyu+, was published from April 10, 2015, to February 22, 2019; on that same day, a fifth part of Senyu started.

Haruhara published a print version of the series in Shueisha's shōnen manga magazine Jump Square from May 2, 2012, to April 4, 2013. Its chapters were collected in two tankōbon volumes, released on December 4, 2012, and July 4, 2013.