Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 17 - 17-7. Reason Behind the Taboo

Karsha, a general in the United States Army, was a loving father and husband who was accused of killing his wife and two children. As a result, he was sentenced to death. However, his life took a turn when a sinister being transmigrated his soul to a world of cultivation. He awakened as a slave and slowly rose through the ranks thanks to a strange system with its own agenda. He began walking the path of cultivation and immortality, which will soon drive him into a conspiracy so grand that his understanding of who he was, who he is, and who he is to become will be put into question.

Childhood sweethearts.
The most popular person in school is my childhood sweetheart.

- Description from Novelupdates

While on a school field trip in the Czech Republic, Kang Hyuk happens to stumble into a shop called “Archmage.” To his disbelief, the shop is actually owned by an archmage… from another world! Forced to become the Archmage’s disciple, Kang Hyuk is punted into the Kallian Continent, where might and magic overwhelm and wyverns fly high in the sky…

In this world, people are either sword-wielding knights, magic-wielding mages, or spirit-wielding summoners. There hasn’t been anyone yet who can do all three… until now.

Li Yi once lived the dream of every pro gamer. He was at the top of his game with the best equipment, the highest stats, and everything a gamer could ever hope for. However, he soon realized that none of his ill-gotten gains for his to keep when he was branded Public Enemy Number One and killed in the biggest battle of the ages.