[MrTerrorist]

Now this is interesting. Modern Military vs High Fantasy Races.

From what i understand from Google Translate, the story goes something like this:

In August 20XX, a mysterious gate suddenly appeared in Ginza, Tokyo where an army of knights suddenly invaded and killing many people. The Japanese government in response sends in the JSDF to fights off these "invaders" and finally driving them back to the Gate in 7 days. This incident becomes known as "The Ginza Incident".

After taking over the Gate, the JSDF sends in a recon group to explore the world beyond the Gate and try to establish diplomatic relationships with the people there. The protagonist is Yohji Itami, a recently promoted Captain in the JSDF who is a member of the recon group sent to explore the world. Along the way he meets a witch, a high elf and a demigod who are part of a resistance against an Evil Empire, the same empire that invaded Earth. While Yohji helps the local resistance fight against the Empire, back at Earth, the nations of the world are putting pressure on Japan to share information about the Gate with them....

Fun fact: The author of these novels is an ex-JSDF servicemen.