Anime Masterminds: The smartest anime characters meet! (Doujinshi) - Vol. 1 Ch. 18 - That is what our task is...

[MangaDex]

 

[Outflanks10]

The 3 that are working together are Light Yagami, Ryuk & Sōsuke Aizen as they are the only 3 that know Ryuk's exists.
Thus they are working together by not saying anything about it.

Thanks for the translation Mangás em Minutos

 

[Ernergeycey]

Amazing