Death Note - Episode 18

You can play the game with them and try to figure whos kira among them

when they refer to different “kiras” i think they mean one person controlling things behind the scenes, however when they refer to “this kira” or “the old kira” or “the new kira” they mean who the person behind the scenes is controlling. When L said something like “this kira has a different goal” i think he means that the mastermind is using this new kira for a different goal, but it’s all still the same kira, just passing from person to person.

i do appreciate that the show took some time to show us more about the supporting characters than just have them be npc plot devices. They aren't the most fleshed out side characters out there but theres enough to understand their motivations.

It may feel very dense now, especially with the Yotsuba group stuff, but it does wrap up nicely, explanations are given in a later episode!