Tate no Yuusha no Nariagari, Shinchou Yuusha: Kono Yuusha ga Ore Tueee Kuse ni Shinchou Sugiru Recommendations
Isekai anime about overly serious main characters with ridiculous amounts of ability.
Both feature a male hero protagonist who level up and fight monsters in the process. Cautious hero is more of a comedy, where Seiya is overpowered yet naive, whereas Shield Hero has more serious tones as Naofumi is looked down on and works his way up the ranks. The both are hard to open up to. Both of these anime feature the protagonist being transported into a new world (isekai)
Both Protagonists personalities match each others, also they both are cautious with people because of the fear of loosing and being cheated
Protagonists were summoned to another world. The main characters have some dark personality based on their past. Heroes become overpowered, they're kinda smart.