Re:Monster

In both shows the main character dies and gets reincarnated as a monster. both of them lead their horde of monsters and constantly receives power ups by consuming defeated enemies. Both mcs also can eovlve into stronger forms when reaching certain levels.  

If you love the base building / domain upgrading animes this is for you smilarities : both isekai both Strong MC both live with monsters both are leasers of their people 

In the storyline has similarities, such as the main character experiencing growth over time, getting different powers, besides having several subordinates. In addition, the character has memories after reincarnation to be non-human. 

both: - resurected as weak monsters in another world - get much stronger compared with the rest and lead them - evolve differences: - one is more comedic with much more self centered MC whiled the other accentuates the growth of the other characters along with the MC 

although very different the two main character are very similar Lugh and Goburo are very similar both where fighters/ assassins in their last life killed on the battlefield both are reincarnated with their skills from their last life both are very tactical aware and cruel to protect themselves or farther their goals both have parts of their body altered one with surgery and the other a prosthetic arm that enhanced their bodies  

While fundamentally different in tone, design, and plot, there are a lot of similarities between both Solo Leveling & Re:Monster. Each protagonist starts with nothing and through leveling-up, unlocks game-like abilities with a key point being controlling others. Whereas Rou is born into the new world and levels up via eating, Sung Jinwoo levels up via fighting but unlocks abilities in almost an exact scenario that's displayed like a video game. Both series have each protagonist taking up leadership over a group of other creatures and using them to fight and continue growing. As they grow, their appearances change and become significantly "cooler," "mature," and "more attractive" to match their evolution. As far as their respective English Dubs, both characters are voiced by different VAs, but sound very similar to each other in their presentation. read more 

If you like the mechanic of the MC defeating monsters to steal their skills then this could be for you. The plot is not very similar.