The Beginning of the End (オワリノハジマリ, Owari no Hajimari) is the first episode in Japan Sinks: 2020.
On the plane, the pilot instructs the passengers to put their seat-belts as they are landing in 15 minutes in Tokyo. Mari Mutoh enjoys the view from the plane and takes some pictures. Elsewhere, Ayumu Mutoh and others from her team practice in the stadium and their coach informs who will be participating in the 400-meter relay race. A big earthquake hits Tokyo and Go Mutoh doesn't realize it until his lunch falls from the table. At a different stadium, Koichiro Mutoh works as constructor and they decided to finish the lights and call it a day.
Ayumu's coach decide to stop the practice for the day and the girls go in the locker room to change clothes. They receive message for incoming earthquake and think its just the aftershock, but then a stronger and more destructive earthquake hits them. When Ayumu opens her eyes, she sees all the destruction and dead friends. An injured girl asks her for help, but she panics and runs towards home. Go got injured and recalls what his father told him and tries to get outside. Koichiro survived without injuries as his safety ropes kept him from falling down. He gets on his scooter and heads home, but then a building collapses and falls on the bridge he is on. The plane was damaged and had to emergency land in the river. While the people evacuate from it, they see incoming tsunami and Mari jumps in the water, but sees a kid drowning and helps it.
Ayumu reaches their home, but as no one is there, she goes to the nearby school yard, where people had gathered. She calls for her family, but is unable to find anyone. She sees a colorful lights at the hill and is reminded of how her father illuminated their plants. Running there, she finds her father who explains he also went home and couldn't find Go there. While waiting, Ayumu sees some people she knows and then sees Nanami carrying Go. As they look at his injury, their mother Mari also arrives.
Looking at Tokyo from the hill, they see the city is burning and it's flooded. Mari is glad that they are alive and together and wants to take pictures along with Haruo Koga and Nanami Miura. But Haruto stays away and doesn't say anything and Nanami decides to take a picture of the family. As signal returns to the phone, Nanami asks Ayumu if she can borrow hers to call her family and Ayumu agrees. Ayumu starts crying for leaving her team behind and not helping her and Mari and Koichiro try to comfort her. In that moment, people fall from the sky and they see a helicopter crashing. As they look up, they see more dead people in the trees.