Oooh, so it's the 今 here but with a different pronunciation. Good to know, thanks.
This is a "Jukujikun/熟字訓", that means the pronunciation of this word is not related with the individual ones, or actually you can say this is an irregular pronunciation. But don't worry, there are not many words of such kind.
I'm not sure, but it may go some way to explaining why a name such as Hikari can be written as 月.
sorry for being childish but as i was reading the hiragara for 'this morning & every moring', i couldnt help but notice it sounds like ' kissa my ass!' when you read it together, hahaha
I have a tip to remember this word: 「けさ」kind of sounds like the singer 'Ke$ha'. Ke$ha has a song called 'Tik Tok' and the first line is 'Wake up in the morning...'. It's a little bit complicated, but it helps me, and I hope it helps you, too. Thanks for reading this! Have a great rest of your day! >w