-> He can lvl-up via his soldiers’ kills. He has thousands of them and they can ”respawn” after 90 days.

Yes, he can lvl up via their kill, but they don't really respawn after 90 days. If an infantry soldier dies, he dies for good. After 90 days, he can summon another infantry soldier to replace the decease, but the summoned one will be someone else.
-> MC only use them as a garrison force, the obvious lvl-up marathon is too complex to think of.

Wrong. MC use his aerial forces to bombard the demon's breeding ground a.k.a spawn points. He levels up with it in the beginning. Next, with no demon left, do you want him to kill ordinary peoples ? MC is ruthless in a battle, but he's very far from cruel.

-> MC want to leave the castle and fight with his subordinates on the front lines while he has the fighting capabilities of a recently conscripted otaku. (A.K.A., none whatsoever). Any random soldier he summon could probably take out a hundred of himself. He’s stupid and suicidal. This novel is a joke and entered my ''sh*tnovels'' list. Thanks Admin for the option of hiding updates from selected reading lists

Really? Have we read the same novel? This happened when MC decided to defend a city from 50 000+ enemies troups. He entered with tanks, heavy weapons, and crushed some enemies before entering the city. He left a couple dozens soldiers outside the walls to defend against the enemy unit, but they get cornered. MC is stronger than his soldier, he can heal any wound (well, as long as he has enough mana), and has the ability to save them without exposing himself to too much dangers. He climbed down the wall with some soldiers, reinforces the surviving soldiers and saved their lives. I see him as a good leader.

Basically, we know nothing about the MC except his name and that he was a typical high school student. After death, he chose 3 skills and get summoned in a demon infested forest.
He establishes a base, summon troups, weapons, supplies etc. After a few fights, and making a secure base, he wanders outside with some tank, MV's and soldiers.
He saves some knights who escort a princess (seen as a cursed child because of her heterochromia). Well, apart from the knights and her mother, she's quite hated. Posing as the chief of an adventurers groups, he gets aquainted with her (yeah, she'll be yandere too, and the process is explained in the side story lol). She grows found of him quickly. After that he goes to the capital to receive compensation, but during his meeting with the Queen, they learn that a city called Fort city is surrounded by the strongest country in the continent. The country is facing destruction if the city falls. The enemy country is heavily magic based, with a racist religion, and backed by other worlders.

MC decide to help this city because the mayor of this city.. Hum. During the travel, he passes by small conquered towns. The inhabitant were killed and their corpses hanged.
He appears outside the cornered city, save the day, raise *yandere* flags but then the ennemy other worlder make his apparition.
He comes along a giant floating island and flying ships, with magical barriers. (Is that really magic omg)

MC no longer hides himself, declare himself as the Excellency/President/King/Emperor of "his country" Parabellum, which devise is "If you want peace, prepare for war", and send his aerial unit bombard the floating island. What magical barriers ? A few rocket and explosives take care of that. The other worlders is scared sh*tless by seeing advanced weaponry, and escape with the damaged island. MC then finishes the 50k+ unit on ground.
His prestige is established.

Afterwards, he make some treaty with the country that was attacked. He accepts to defend them and give logistical help, but won't help in attacking. Except if the enemy send an other worlders. Many things happen (well, many many yandere stuff lol) A dwarf from a neighbooring kingdom come to ask MC for help, telling him that the magic country have developed new weapons, golems, magic guns etc. MC accept to help his country, a country of non-human. Many thing happens again, and a month later MC come to sign a treaty with their demon king. He heals her, (MC can restore cut limb, missing eyes and organs) and gain more respect.
Next, the fight begins. MC had destroyed all the enemy supply routes during the last month. They lack food, so ther intend to ransack a city. MC's artillery and tanks trample the enemy (his commanders note that the enemies are developping strategy to cope with MC's unit, not to avail).

It all started when he saved the carriage of the princess with heterochromia eyes which is treated as disgusting. That loli princess became too attached to him and yea, feels like she's a yandere.
Almost all girls the MC have relation is a yandere.

The one best point here is the liutenant that she summoned is very loyal to him. That she asked the other girls to make the MC feel good, (they did it (͡° ͜ʖ ͡°)). Also seems like the MC's healing magic has a some sort of side effects which make a person he saved look at him like a god.

Since they tell that they are summoned country of otherworlders and the MC is their king

first of MC's powers for summoning people and weapons and facilities are sealed when in battle. So basically speaking if the MC is ambushed he won't be able to summon the supplies and soldiers if there was a suddent trial by the God's or God from that world.

Honestly it didn't bother me much, because well, what do you expect him to look like? Average Japanese high school boy I say. Why is simple, his name is Kazuya Nagato (sounds Japanese enough to me). As for what that means to you, that is up for you to decide, but do you really need some one to describe it to you? And when you think about it, if its written in japan would they necessarily spell out "japanese school boy" to themselves? Just picture our own novels saying "American school boy"... it gets kind of weird, so maybe they didn't expect this to hit it off internationally? I am very glad it is though.

I think its good all his troops seem to basically be yandere for him, wouldn't want to be summoning soldiers that would betray you or disobey you. But at one point... after a huge trial and lots of worry, he just wanted to rest, his advisor suggested he rest first, but he insisted to resupply the troops ordinance first.... As a surprise to help him rest and unwind. Chitose made a suggestion to a small group of female soldiers, and with crazy yandere smiles they acted, though they later hinted ended up the ENTIRETY of the females he summoned... well, basically he got reverse raped by 150 women over the span of 2 days. I laughed so hard and found myself shocked at how fast that escalated, all the more funny though because it all started with him and a high pitched IYAAAA scream when he realized what was about to happen! But whether we should consider him lucky he has 150 beautiful women would just throw themselves at him, or should we despair for him he got reverse raped by 150 beautiful women without rest for 2 days... take that how you will (thank goodness for himself he had stamina and vitality MAX blessings). The male troops in the command center just saluted him and left... he had no idea why, but that just made it funnier.

Chitose even states her very reason for existing is for her master (I think of it in a similar way to Re:Monster creature summons with intelligence) There is one chapter where an adventurer tries to touch her, and it ends with 5 badly beat up adventurers, one of which got flung out a window, and when the protagonist steps in... he sees her with a combat knife ready to slash the guy's throat and the poor sap having already wet himself.

There's also the regal empire on the other side of the world with WW1 technologies fighting their own wars. They're not aware of MC's newly established military nation yet and they probably can't cross the ocean but it'll be very interesting to see them go up against MC's nation. They're probably the only ones as a big threat.

He got outsmarted in volume 3 chapter 12 (I think).