Fuguushoku "Kanteishi" ga Jitsu wa Saikyou Datta

Both MCs are able to train their bodies to peak human and do incredible feats of strength once they get to this point. Both MCs also faced up against insanely strong adversaries at the start of their show and undergo training from a master that is EXTREMELY difficult and strict. Needles to say the HARSH training leads both MCs to being incredibly capable with their abilities.  

Both MCs are betrayed by their party members early on in the series only to find themselves using water with a 100% healing property to level up.Both MCs were given abilities that most would deem useless but in reality actually hold the key to their true strength once they master them. Funny enough the first party member they meet is a super strong yet super short loli! 

Both mc have one of the weakest skill and got exploited and abandoned by their peers then sent to a deep dungeon to fight for their life then got overpowered