The reason is that the Japanese pronunciation of 818 is similar to "はぃばら", so Japanese mourning fans designated this day as "Ashihara Day" to express their feelings for Haibara Ai.
In the famous detective Conan, there is a very popular female character. She usually looks very cold, and once she meets something related to the organization, she becomes nervous. Yes, she is Haibara Ai. August 18th was designated as "Ashihara Day" by fans, and even this day was directly regarded as Xiao Ai's birthday by fans, although Haibara Ai's birthday was not officially announced.
Haibara Ai is actually a very sympathetic character. Her parents and sisters all died because of the black organization. She has no relatives in this world. If it weren't for Conan, the doctor and the members of the juvenile detective team, Ashihara might have been loveless. For Ashara herself, she is lonely, so she needs more care.
As for why Mr. Qingshan didn't announce Xiao Ai's real birthday, it may have the effect of foreshadowing and adding to the mystery of Haibara Ai. As Belmore famously said, "A secret makes a woman woman", secrets can increase women's femininity, which is also applicable to Haibara Ai.
Personality characteristics
Ashihara is a talented medical chemist and pharmacologist, and he is also good at many sciences. His thoughts are always elusive and unusually calm (but he will lose his calm once he meets something about the black organization or Higo Ryuusuke). His cold appearance hides mysterious charm, hazy kindness, cold innocence and some rebellious thoughts.
his mouth is not forgiving, but his will is not strong enough and he has a lot of personality. Ashara's personality is very cold and withdrawn, and he has a completely different sense of maturity from his peers (obvious in the early stage and gradually improved in the later stage). Like an iceberg, she also calls herself a "shark from the deep sea".
She is a completely different girl from Mao Lilan. Although her appearance is strong, her heart is very fragile. Under the hard-working appearance, she is just a girl who can feel warm and lonely after hearing her sister's message for 1 seconds. But since she came into contact with Conan, her cold heart seems to have begun to melt, and with the feelings and happy smiles of ordinary women, she began to have a lovely side.