Hyakuren no Haou to Seiyaku no Valkyria

Both of these animes share a lot of similar overhanging themes and details. -Person in a strange world -Smartphone is the only thing still with the Protagonist in this new world -Protagonist uses a smartphone to create items from their world to progress their new world -Build a harem, lots o' lolis -Protagonist is uninterested in his harem and his harem is in love with him 

In both isekai's, the protagonist is able to use knowledge from the real world (Smartphone and internet in Valkyria and former game dev in Death March) in order to benefit themselves in the new world. Both shows also consist of a massive harem, with new members getting added along the way through the 'heroics' of the MC 

The main character was from the world where we live in and posses knowledge on how to win a battle with tactics. Both participate in numerous of battles and using techniques learn from history books. 

Underpowered protag, who uses his knowledge of his home world to rebuild the nation he's transported to, in order to make it stronger. 

The same fantasy based anime that involves chacater stuck in a alternate world, it also has the same situation where guy has a harem except one has it harem added from time to time while the other ony has 2 girls as the guy's harem. 

In both series the MC is a strategist, who doesn't excells at physichal combat. 

Similarities: -Guy got transported into another world by some magical instrument. -Both instances, guy has to adapt to the new world he is in. -Both have the same situation where guy has to use his wits if he is to survived that world.  

With other-worldy knowledge, the main character are set on a quest to dominate the world! 

It was both having fight between soldiers. Both travelers from these animes have supreme knowledge about the art of war, and the proper equipment used in wars. 

After being called to a warring country in need of a hero, our isekai protagonists look for a way to return home while growing closer to the people they're fighting for. Throughout their respective journeys, we get to know more about the world and the characters surrounding the protagonist. In contrast to the bloody, calculated wars of Hyakuren, the world of Dog Days has an approach to war that could only be described as fun - featuring colorful art, announcers, and protection magic. Since this hero is a frontline fighter and not a ruler, more focus is put on the action and show that he puts on. Give Dog Days a try if you want a well-done, but not overly serious take on what it means to fight for something. read more 

The main characters have the knowledge of the future to help them conquer the world. "Hyakuren no Haou to Seiyaku no Valkyria" is a rather bland ecchi while "No Game No Life" is on a "Log Horizon" level. 

Both main character is like a war hero, they defeated every opponent by displaying unique war tactics and somewhat by winning a war, it will lead to winning the heart of the girls too.