Seinosuke Andō is a main human character in the second part of Lassie.
He meets Masumi in a rainy night when she tries to help a Shiba mix puppy. They fall in love and adopt the puppy, Chiyomaru. They tpgether open an Italian resturant and runs it together before Seinosuke starts cheating and seeing Machiko. When Masumi passes away, Sanosuke is caught by grief seeks comfort in the arms of the another woman, Machiko, and marries her.
One day, Seinosuke discovers that his beloved dog, Chiyomaru has run away. Desperately he posts searching posters all over town, but without result. After a fight with Machiko, he visits his wife's grave to pay respect to her. Out of nowhere, his dog Chiyomaru jumps out and into his arms. Beside his dog is a young Collie. The dogs then runs off with Seinosuke following it. He finds out that Machiko has tried to steal his money and divorces her.
Afterwards, Seinosuke takes home the two dogs and takes care of them. He calls the local petstore to hear if they are missing a Collie. To his surprise, a girl answers the phone. The girl's name was Akutsu and she had been looking for the dog. Seinosuke reunited them both.