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.

Before meeting in the science world, Senku is shown to have either read/heard about Gen’s psychology books, criticizing them for being trashy.

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

It is shown, however, that Gen didn’t truly believe that Senku would make him cola and instead had his personal reasons for joining the Science Kingdom.

Senku tells the others that Gen’s trust has been secured since he’d seen Senku create a generator, while Gen illustrates his feelings in the episode featuring Senku’s birthday.

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. Senku, on the other hand, struggles with bargains and trades as shown with his bluntness extracting information from Luna.

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.

In the Stone Wars arc, Gen seeks out Senku to put together a secret plan to trick Tsukasa’s kingdom into believing the United States is up and running. Gen proclaims that “Ishigami Senkuu and Asagiri Gen will happily fall into hell together” due to the deviousness of their plan. The moment is interrupted by a curious Chrome, with the meeting ending in a three-way fist bump.

In the Dr. Stone Light Novel (because there is no official English translation, information is collected from fan translations and may be subject to errors) Before Tsukasa is cryogenically frozen to prevent him from dying from his wounds, Gen asks Senku to allow him and Mirai to visit Tsukasa. This is in violation of Senku’s previous no visitor policy, which he lifts upon Gen’s request. The light novel illustrates Gen’s concern for Senku’s nervousness about Tsukasa’s life, and it is stated that Gen decides to do this to lift some of the guilt and worry off of Senku’s shoulders so they share the weight of responsibility. Senku and Gen are also implied to share a room together in the village.

As the manga progresses, the pair repeatedly demonstrates their trust in each other’s loyalty and ability in their respective fields.

When Ryusui requests Gen’s presence on the Perseus as they prepare to set sail, Senku remarks that Gen’s mentalist abilities are important for handling whatever they run into on their journey. In return, Gen reasons that wherever Senku is is probably the safest place to be. Kohaku remarks that “The premise of evil is a shady man’s pride“, which may imply that Gen’s intentions when joining the Perseus crew are not what they seem.

After Ryusui and Gen face off against Kohaku and Senku in a card game determining the course of the Perseus, Ukyo questions whether Gen had really planned the whole stunt all along to get everybody on board with the same plan. To this, Gen replies: “Utter nonsense, my dear Ukyo. You’re overthinking it~ However, I will say this. I was giving it my all and then some during that poker game. It wouldn’t have been exciting otherwise. So if nothing else, my loss was a bit frustrating. My dear Senku.”

While Gen seems to feel bittersweet about the loss, he is not shown to harbor any grudges against Senku. Instead, he chooses to prove his own mentalist ability by facing Dr. Xeno and Stanley in their kingdom as a spy.

As of latest, Gen has taken to infiltrating the opposing science kingdom led by Dr. Xeno to take it over for Senku’s own science squad. Senku remarks that “(Senku doesn’t) need stinking instincts to know it’s ten billion percent option B (Gen has infiltrated Dr. Xeno’s kingdom, rather than getting kidnapped)“.

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.
 * Senku almost always refers to Gen as “The Mentalist”
 * they are both part of the five generals