We needs a real bingo book. The kage/anbu leader would be able to put in up to 3 ppl from every village but in total only 6 players. Aside from stat cards, kage or AL could also write additional info about them. Additionaly anbus would then be able to take A rank missions to kill the ppl on the list. If you want to go further you could also add in jails in each village so that the mission would be to capture them. Upon "killing" the anbu would have 30 sec to get the corpse into the village. If it succeeds the enemy is put into the jail with 2x or even 2.5x hosp time. If the 30 sec are over or the anbu is killed the enemy is sent to their hosp with normal hosp time.
Aside from the 6 players, kage/AL would be able to also add in all akatsuki members. These missions should count as S rank.
If you want to go further with the jail idea, dying inside enemy village village would auto send you to their jail with 1.5x of your normal hosp time.
And ofc ppl should be able to free their allies from the jail. It would work like the bandum capping system. Standing still for 10 sec in front of the jail door would free them, sending them to their hosp (For examlpe my normal hosp time is 80 sec. If I was captured and have been in jail for 50 sec, freeing me would send me to hosp with 30 sec hosp time left. So that you have to serve your normal hosp time no matter what.)
Each village should have different jails for every other village and akatsuki. So that ppl can choose to free only their own villagers or also other villagers/akats.
And ofc akatsuki could have the same. One AL or Kage from each village + 3 whoever they want. Its less than villages because akat usually got the strongest ppl. So giving them more they could probably get half of the server into their jail