Before I start let me say that the verse of League of Legends is a Multiverse, this is because of the different events that have happened over time and Ekko's time jumps. Also if anyone needs more clarity ask and i will clarify.
5. Aatrox
Number 5 Aatrox. For the explanation Aatrox can essentially kill abstract and non-copreal beings and able to reach higher beings with his attacks. Also note that Aatrox is immortal in multiple ways as a darkin. Aatrox is also immune to the effects of the void as are other beings on this tier list I am putting Aatrox at the number 5 placement because of the fact that his state can go from being able to destroy countries to solar-systems.
4. Xerath
I am putting Xerath at number 4 because of the fact that Xerath is not only one of the most powerful ascended but also a being that can warp space and time, biology and many other things. Yes Xerath is immortal and with his power will likely not see kindred for a long time. Xerath essentially comes out as your highly op mage in the end.
3. Pantheon
Pantheon is number 3. Going off of lore and info about Pantheon he is most likely the most powerful actual warrior in League currently. Like Xerath, Pantheon can also warp space and time, generate celestial fire and can resist manipulation of his body. Overall Pantheon is essentially part of the aspect of war, and seeks to fight other divine beings.
2. Aurelion Sol
Tbh most of you probably though the big boy would get the number 1 spot but no. Aurelion Sol is likely the most known god tier character in League. Aurelion Sol can warp reality, space and time, and everything else you see and touch. Aurelion Sol is as old as the main universe of League itself and from that is most likely smarter then the majority of other characters. Aurelion Sol does not actually need air, sleep or food to live and can resist the abilities of mostly everyone on this list.
1. Kindred
Yea bet all of yall did not see this coming. To explain Kindred is literally death itself, yea not the grim reaper but the concept of death itself. Kindred only appears to beings right before they die and can kill anything and yes this includes immortal beings as most of them only have long life. Kindred can not actually be killed much less interacted with, the only interaction being in the spirit realm (spirit blossom lore). It is also known that Kindred exists across all Universes of League of Legends, meaning that no nothing is actually immune to it. If you want to argue that Kindred cant kill aurelion sol, thats just because aurelion sol has nothing (other then kindred) that can actually kill it.