Nemesises? Nemesi? Whatever. I want to read novels where mc has a very long time nemesis and they are very close to each other in terms of advantages and disadvantages all the time, without certanty who will win eventually, where they really fight with their all. Bonus points where they both are schemers and there are lots of twists. Even better if they have to cooperate at times to face a common threat but then nonchalantly return to going at each other's throats