Synopsis
In the current time Thanos is making a yearly pilgrimage to the ruins of Titan, not to celebrate his destructive victory but to visit his mother's grave and remember his past.
In that past the Eternal Sui-San is giving birth to a baby who looks more like a Deviant. A'Lars (Mentor) sees a child who has survived despite bring tangled up in the umbilical cord, and names him Thanos. But when his wife sees the baby she tries to kill it with a scalpel because she sees death in its eyes. They have to sedate her.
Young Thanos is a bookish loner. But 1 day a group of youths approach him commenting on his weird looks. He calmly explains it's a genetic mutation and isn't catching. They ask him if he's Mentor's son, but he suggests they really want his popular brother Eros and offers to introduce them to him. They reply that they're interested in *him*, reportedly the smartest kid in school. They ask if he wants to play with them. Thanos drops his notebook and joins them. We see that he has been sketching a nearby dead and decaying animal.
Later the boy tells his father his plan for the annual school celebration of science. For his part he intends to describe how his genetics make him appear different. He asks for access to his family files. And would also be interested in hearing how his parents met. But Mentor is too busy working to listen.
He visits Sui-San who is confined in a straitjacket and won't look at him. He tells her of a recurring dream he's had for 4 years. In it someone tries to stab him as a newborn. But also he sees himself grown up and using the same knife to ... But he says he's solved that problem by never sleeping. He also tells his mother that he's planning to ask a girl to be his girlfriend. He's created his own breed of flower to give her. He'll bring some to Sui-San too and maybe it'll help her get better so she can come home.
Thanos is playing a ball game with some boys. Some girls are watching and talking about him with mixed opinions. Strangely they don't know his name until another girl approaches them and tells them it's Thanos. She expresses much interest in the boy.
The next scene is a science class at school where they're going to dissect some lizard-like creatures (which appear to be the species Thanos was drawing earlier). Thanos has to run from the room vomiting. The mystery girl from the previous paragraph accosts him and says that dissection will get easier with practice, but Thanos claims to never want to cut open any living thing. She says he'll have to do things like that if he wants to be a great scientist like his father. Thanos is unsure *what* he wants to be, and she recommends a place she knows where he can get away to think.
Thanos leads some friends to the cave system she described. Apparently there are some jewelled formations there and they might find some gems. But then a rock fall separates him from his pals. He's trapped with only those lizards for company. It takes him 3 days to dig his way out, and the lizards seem to show him the right path. But when he reaches the others he finds them dead, and the lizards are eating their flesh.
Young Thanos becomes a loner again. His classmates whisper about what happened and the mystery girl joins in. Later she urges the boy to go back to the cave for revenge for his fallen friends. He takes a knife with him and slashes many lizards to pieces.