The Master Of Ragnarok and Blesser Of Einherjar started off as a light novel series written by Seiichi Takayama and illustrated by Yukisan. Then a manga adaptation was created by Channy being published by Hobby Japan. And finally with an anime adaptation directed by Kōsuke Kobayashi and under the studio EMT Squared.
This anime takes place in a world called Yggdrasil sometime in the bronze age where many clans fight against each other in war for conquest. There are those that are born with magical powers called Runes that can turn the tides in the battlefield in which they are called Einherjars.
After the main character, Yuuto Suoh, took a selfie with a divine mirror, he was instantly transported into Yggdrasil. And from there has became the patriarch of the Wolf Clan in which, thanks to his great knowledge and smart phone, was able to evolve the clan's technology to win battles; being ahead of the bronze age.
It all starts off to where we see Yuuto commanding his force of soldiers along with one of his Einherjars Felicia, his oath-sworn sister, against the Horn clan. From there we get to see soldiers using the phalanx formation against the enemy thanks to Yuuto's bright knowledge of warfare.
From there, the Horn clan lost the battle and Yuuto's other Einherjar, Sigrun, captures the Horn Clan's Patriarch, Linnea. She is taken to Yuuto's military camp in which she had to agree to become his sister by oath or else would burn the Horn clan's capitol to the ground.
Upon his return to the capital of the Wolf Clan, we see him going up to the temple to make a call to his childhood friend, Mitsuki Shimoya. This is possible due to his phone being solar powered as well as being connected with the divine mirrors from both worlds.
And from there we see continuous evolution of war technology thanks to Yuuto as well as him forming more allies from different clans and creating good bonds between them. As well as more progressively-tougher enemies come into play for him to face.
The Master Of Ragnarok Opening
It's quite reasonable as to why the first episode doesn't start off with him taking the selfie and being transported to Yggdrasil but rather going straight to the battlefield where he's already a Patriarch few years later. This is so that we get to see his leadership skills in play as well as his great knowledge being put on display.
Not only that but being able to see him establish oath relationships with other patriarchs and starting his own harem. It would be boring to see him upon his first days being adopted into Felicia's family as we may not see much from there at the beginning.
Yuuto displays a great role as a leader for the Wolf Clan. He considers himself being a "cheater" due to being from a different era and having historical knowledge. But what he doesn't realize is the potential he has for making his own clan great as it takes not just knowledge but also someone who puts great, organized use to it.
There may even be some historical accounts in history of warfare that viewers may not have known before, in which this anime can be a fun way to learn about ancient warfare such as with the intermission credits on display for viewers to read off of the characters' backgrounds and weapons/historical events that took place long ago.
Felicia
Phalanxes
The harem element brings in plenty of humor as every family-oath-sworn girl apparently wants to be more than adopted family as they may even try to get more intimate with Yuuto. Yet with all his might, just resists the temptation and often pushes it aside.
Master Of Ragnarok Episode 1 "Getting Rid Of Energy"
This anime is highly recommended for fellow Isekai fans as this one seems special enough to stand out with not only being transported to another world with his own harem, but being a leader in the bronze age that continuously brings up not only new warfare technology but other pieces of work for his city state such as agriculture.
In fact, he hardly uses his phone to look up historical events, weapons, etc. as he is equipped with vast knowledge of historical accounts and innovations.