Enneaphobia

Nonaphobia (from Greek nona meaning "nine") is the fear of number nine. It is a rare phobia and it is not recognize by the medical literature.

Nonaphobia may commonly be triggered due to being disappointed of achieving near perfect scores or near-completions, like achieving 9/10 in the quiz often but rarely getting 10/10, achieving 99% in the video game but couldn't go any further, or even seeing a grandparent or great-grandparent dying at age 99. 99-year olds may commonly have this fear until they make it to 100. The fear could even be due to some mathematical uniqueness of the number nine, like dividing a number by nine or nine-only number (e.g. 999) whose both numbers containing same number of digits would result in the number repeating itself (e.g. 32/99=0.323232...), leading them to have negative thoughts about infinity and possibly leading to apeirophobia.

Nonaphobia is usually not a severe phobia, but sufferers would often avoid the triggers. Nonaphobes would try to avoid encountering the number that ends with nine especially, e.g. 39, 449. A nonaphobe may not like to live in the house that has the address ending with nine. Nonaphobes who are baseball fans would think that the games should last 10 innings instead of 9, and so they could lose interest in baseball. Sufferers may not mind to chronologically assign the age ending with nine.