The term 520, an abbreviation for May 20, denotes an unofficial Valentine's Day in China. The number “520” phonetically resembles “I Love You” in Chinese.

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So, Neo chooses to propose to Hannah on this date because it could be transform into a day filled with romance and affection! Hannah loves hand written letter, but Neo has never done it. During the proposal, when Hannah received the love letter, she was so surprised and touched. Even if it is simply a letter, Hannah is moved by it.

 

Besides, she also loved the decorations and everything arranged by Neo. Therefore Neo appreciated the presence of Hannah as Hannah has always stood by her side when he only had little in life.

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With that said, Neo, who is not typically romantic, clearly put a lot of work into making Hannah practically tear up throughout the entire proposal. Sometimes the most significant events in life occasionally only need to occur once.