Total babies named Kosei (all years): 90
| Year | Boys (count / rank / %) |
|---|---|
| 2020 | 7 / #10145 / 0.000% |
| 2019 | 5 / #13236 / 0.000% |
| 2018 | 6 / #11554 / 0.000% |
| 2016 | 5 / #13347 / 0.000% |
| 2014 | 5 / #13182 / 0.000% |
| 2013 | 6 / #11545 / 0.000% |
| 2012 | 5 / #13349 / 0.000% |
| 2011 | 5 / #13463 / 0.000% |
| 2010 | 6 / #11576 / 0.000% |
| 2009 | 6 / #11824 / 0.000% |
| Year | Boys (count / rank / %) |
|---|---|
| 2008 | 9 / #8703 / 0.000% |
| 2006 | 5 / #13158 / 0.000% |
| 2004 | 5 / #12404 / 0.000% |
| 2003 | 5 / #11949 / 0.000% |
| 2002 | 5 / #11708 / 0.000% |
| 2000 | 5 / #11406 / 0.000% |