Although Fang Zheng wasn't really interested at first, he eventually decided to go to Mermaid Island with Heiji Hattori and Conan to see how they would handle this matter.
But to be honest, although Fang Zheng knew that Monshaku Saori was quite timid, he didn't expect her to be this cowardly. According to Heiji Hattori, the letter was sent to his house three days ago. Based on the timeline, it means that Monshaku Saori realized the Mermaid's Arrow she drew was missing a day before Fang Zheng found out about it, and then went to find Kimi Shima to self-detonate, then wrote a letter to Heiji Hattori for help on the same day......…
This desperation to survive is way too strong.
However, she was sunk into the sea by Fang Zheng the next day, indicating that being too desperate to survive isn't necessarily a good thing.
