1. きら (kira): This is the most common way to write "kira", and it is usually used for the word "sparkle" or "glitter".
2. キラ (Kira): This is a less common way to write "kira", and it is usually used for a name or a brand name.
The choice of which one to use depends on the context. If you are referring to the word "sparkle" or "glitter", then you should use "きら". If you are referring to a name or a brand name, then you should use "キラ".
Here are some examples:
* きらきら光る (kirakira hikaru): This means "sparkle brightly".
* キラ先生 (Kira sensei): This means "Mr. or Ms. Kira".
* キラッ (kira!): This is a sound effect that means "sparkle!"
It is also important to note that the pronunciation of "kira" can vary slightly depending on the context. For example, in the word "きらきら", the "ra" sound is pronounced more like a "la" sound.
Ultimately, the best way to write "kira" is to consider the context and choose the appropriate spelling and pronunciation.