Hi hope this helps, "Approximately 100 years before the current story line, a young Hisagi and several of his playmates fell prey to a Hollow attack in Rukongai. Luckily, it wasn't long until they were saved by Kensei Muguruma and the 9th Division. After defeating the Hollow, Kensei attempted to cheer Hisagi up (albeit with a slightly scary smile and demanding manner) and asked his name. This was when Hisagi saw Kensei's "69" tattoo on his chest and acquired the inspiration to get the same tattoo on his cheek." (Bleach wikia).