[name_m]Kester[/name_m] is an [name_f]English[/name_f] nickname for [name_m]Christopher[/name_m] 
I like the suggestions of [name_m]Kitto[/name_m], [name_m]Cap[/name_m] and [name_m]Kip[/name_m] suggestions by others.
A few more ideas:
[name_m]Captain[/name_m]
[name_m]Crosby[/name_m] / Crosbi / [name_m]Crosbie[/name_m]
[name_m]Richie[/name_m]
[name_m]Ricky[/name_m]
[name_m]Tor[/name_m] / [name_m]Thor[/name_m]