We really like the name [name_u]Kai[/name_u] but would like to make it longer. I also like the spelling of [name_u]Kai[/name_u]. If we made it longer to [name_m]Kyson[/name_m], do you think the spelling of Kaisen would sound too made up.
Please help!
I would pronounce [name_m]Kaison[/name_m] as [name_u]KAY[/name_u]-son, so I would go with [name_m]Kyson[/name_m] for the pronunciation you’re wanting.
I like the name! I think Kaisen might be mispronounced sometimes like [name_m]Kayson[/name_m]. My son is [name_m]Rayan[/name_m] and he gets called [name_u]Ryan[/name_u] all the time, even though the first syllable is pronounced [name_u]Ray[/name_u] like it’s spelled. And I thought it would easy for people! [name_m]Just[/name_m] something to keep in mind. If you want to spell the nickname [name_u]Kai[/name_u], then Kaisen makes more sense. But the nickname is equally nice spelled [name_m]Ky[/name_m]. Good luck! 
I prefer the look of Kaisen to [name_m]Kyson[/name_m]. I would assume it’s pronounced the way you intend. But I think both [name_u]Kai[/name_u] and [name_m]Ky[/name_m] are cute. I know a little Kydan… [name_m]Kaiden[/name_m] might interest you.
My first instinct would be to pronounce Kaisen like [name_u]Kay[/name_u]-son, but the pronunciation you’re looking for also makes sense and I think most people who know your son would hear his name before they saw it written down, so it wouldn’t be a big deal. Aesthetically speaking, I think Kaisen looks nicer than [name_m]Kyson[/name_m].
Why not just name him [name_u]Kai[/name_u]?
[name_m]Kyson[/name_m] is most likely to get the pronunciation you want. I wouldn’t know what to do with Kaisen. I would probably assume it was supposed to be [name_m]Kayson[/name_m].