Sengen

Sengen is the slash ship between Senku Ishigami and Gen Asagiri from the Dr. Stone fandom.

Canon
Initially, Gen was sent by Tsukasa as a spy to confirm Senku's death. The two had apparently already met prior to the Kingdom of Science and were classmates. Their beliefs and ideologies puts them on opposite ends of the argument, with Senku taking the more logical and scientific side and Gen preferring to use manipulation and tricks. Essentially, Senku is a scientist while Gen is a self-proclaimed mentalist.

Despite Tsukasa being the one who revived him, Gen betrays him for the Kingdom of Science (Senku) because Senku promised to make him cola.

Gen and Senku become close friends despite the former's manipulation. After Gen defects to join the Kingdom of Science, Senku recreates Gen's favorite drink, cola.

Gen uses innocent leading questions with Senku in an effort to figure out his birthday. He then had the Ishigami village help him build an observatory for the occasion.

When Senku is brought to said observatory blindfolded, he assumes that the Ishigami village had figured out that by working with Gen and handing Senku's head to Tsukasa would mean the village is safe. Gen states that he has 'no idea what [he's] talking about'.

Senku asks Gen how he knew it was his birthday, as he hadn't mentioned the date beforehand, and reveals that he saw that Senku wrote the day his petrification was undone when he woke up. Gen goes on to say; 'Since before I met you... I've been rather fond of you, Senku-chan, setting aside personal gains.'

Senku often schemes with Gen and the two are shown to have a large amount of trust between them. Senku and Gen are shown to be intellectual equals, but Gen is more skilled in psychology and the art of manipulation. He tends to not know much about the science behind Senku's inventions.

More than once, Gen is shown to be fascinated by Senku's inventions and holds great faith in his ability to restore humanity. Senku does point out that Gen is not completely devoid of a moral compass, despite Gen claiming to be the most shallow man he'll ever meet.

There are also passing moments where the two of them can be seen together, such as sleeping in the observatory and generally being close to one another.

Fanon
On AO3, it's the most written ship for both characters as well the most written ship in the Dr. Stone fandom.

Fandom
FAN FICTION

DEVIANT ART

TUMBLR

Trivia

 * Both are geniuses in their own right, Senku's a prodigy with it comes to engineering and science; while Gen is considered by both Senku and Tsukasa to be the best at tactics and deception.