Girl and Science
In which our mc lives in a world of magic. One day, while he and his powerful best friend are getting chased (for no apparent reason other than to be chased), they get summoned to another world as test subjects, separated. Mc is summoned by a seemingly sadistic (not like the BDSM bondage type. More like her personality) lady and as a weak person, has to face many troubles. However, after consuming a drink said to make him stronger (more specifically "evolve"), he gets much stronger than before.
Isekai Yakkyoku
In which our mc gets isekaied into another world from overworking. He is now a small boy and decides to open a pharmacy since medicine is only available to the rich, and he wants to make medicine for the poor. Also, he becomes hella op. Did I mention that? Four star for not doing the plot well.
Haken No Kouki Altina (novel)
In which mc, a failed soldier, did something wrong and so, is forced to go to the frontlines. One day, he is transporting a civilian somewhere, and they get attacked. Although weak, he attempts to protect her, but finds out that the "civilian" is actually a princess known for fighting with a large sword. When the attackers are defeated, the princess offers mc the position of strategist/tactician for the army. At first, I thought it was hella slow. However, it gets better and better. A total must read. (I also have a guilty pleasure of strong girls and weak, but smart, boys. Ehehehehe...)
Isekai de Tadahitori no Mamono Tsukai ~ Tenshoku Shitara Maou ni Machigawa Remashita
Battle in 5 seconds after meeting