Amakawa Haruto has someone he always cherished and love, his childhood friend. Even if they were separated in their childhood, He always think about her, put all effort to fulfill the promise they had made. Haruto learned martial arts, so that he can protect her. Haruto learned cooking, spending time her in the kitchen is blissful, doing house chores, working in the farm, study diligently, anything he would do even if his dream is not certain to be fulfiled, yet he keep believing in that future. Acknowledging Haruto's effort, his father gave the permission for Haruto to enter the high-school near his childhood friend residence. That high-school would be a deep reunion for Haruto, his childhood friend, unexpectedly, also attend the same school. Thump, he could feel his heart throb, that's right, there's no way he would mistake her for anyone else, it's her, an important existence who is far yet so close to him. Haruto delighted in joy of another meeting with her, and at the same time, curses fate.

Walking on her side, are an unknown guy.

Haruto became scared, what if they're going out? Having that thought flashed his mind, he don't have the courage to call out to her. Looking from faraway, troubled by his own problem, these days continues until she suddenly disappear.

From that day on, Haruto worried change ito neverending regret. The first day he know she gone, he realized the big mistake he made.
His heart feels like going to break, scream of grief, sorrow, bitterness, stirred through his entire body. However, he wouldn't give up. He can't give up. Not a chance he would give up. He still haven't confessed his feeling. With dim hope he might find her in Tokyo, Haruto moved out from his house and attend the university there.

Three years has past since Haruto entered university. Not even once he forget about her. Between his studies and part-time jobs, he would ask the police to investigate it, even went so far to search her by himself, by foot if he must. But all just wrapped to a mystery. Today, Haruto is taking the bus on his way to home. It's before evening, and at this time, there's only few person inside. Haruto sit there and silently gaze at the scenery outside the window. Suddenly his view shaked, the bus is taking an impact, and Haruto's consciousness goes blank in an instant. The next time he wake up, he is not himself. He is a boy, 7 years old, named, "Lio". On his surrounding, are dirty and smelly... Slums. Haruto soon found himself on a different world than his, harsher and more dangerous. In his mind, are wish to see his beloved one more time, and the wish, to exact revenge on scum who killed his mother in front of him...

While he is not exactly OP in the abnormal way like many Protagonists in other Narou series, he is pretty much getting stronger faster than anyone in the series the normal way because of his huge amount of Mana(? Not exactly sure what is the parameter of the strength here) and his quick witting and hard working mindset (Man he is really an honor student!).
In the current chapter the summoned heroes are pretty much amateur in combat and still naive but thanks to the KamiSou(?) - God's Weapon I guess? they can still pretty much put up a decent fight with a high ranked knight while our MC can handle a horse of high ranked demons on his own without sweating a bit.
When he got measured his own Mana it was said that his Mana had increased a lot comparing when he was 12 years old ( By the way he defeated a high ranked knight without using any weapon at all in the age of 8. Awesome right? If u want more detail keep reading until chap 5 to 9 i remember?). Anyhow his current amount of Mana right now is equal to about 250 ~ 300 mage ( meaning high class magician) which shocked his teacher, the girl who was called the genius among genius mage for having Mana equal to 30 people or less.....

AS for Harem, he is a Ikemen with such a good heart that u may want to change your viewpoint of Ikemen characters~~ Anyhow he pretty much conquer a princess (same age), a teacher (5 years older), a beast girl (self proclaimed imouto 5 years younger), a beast girl, a elf girl, a drwaven girl (all same age), a village girl from his home country( same age who got rejected by him...sad for her....) and lastly a noble girl who is currently helping him( same age)
That is a list of girl in this world, as for in his original world there are his childhood friend and a hero girl who will possibly have interest in him.
Anyhow this guy is very loyal to the childhood even in the new world and when he reunited her again he almost cried in joy.

-Very strong[he learn ancient martial arts from his grandfather in the previous life] so he managed to control his overflowing mana[he got the highest ranking spirit sleep in his body, and he already has unbelieveable mana with that dormant state of his spirit avatar while other Spirit arts user need to awaken their avatar to increase their power]
-versatile in almost all knowledge[fighting, politic, cooking] except for how to handle woman[he is very nice to all of them which resulting in him gathering unknown number of harem].

-Harem?, many woman already lined-up to marry him[teacher(legal loli), little sister(fox eared girl) and four other girls(dwarf girl, an elf, etc from forest), friends of his cousin, daughter of shogun(that shogun said that his daughter can only marry a man stronger than him while he is basically strongest man in east kingdom. but Rio defeated him in sword match, and that match mesmerized the shogun daughter), second princess of bertram.

-but..... his love for his childhood friend made him blind to the affection of the girls surrounding him[the boys treated him as their enemie but not to the pont of hate him]

-at first his teacher magic tool for measuring MP broken by the power level of the summoned heroes
-then she raised the cap, and got their power level

-after Rio brought his teacher out from her house arrest[yeah, he is entering a city full of enemies like walking in the park] she showed that device again to measure Rio power[15 years old]

-But, apparently Rio power is EVEN SURPASSED the new cap level of his teacher magic tool

-Heroes is around 400~~, while Rio is still unmeasured