If you're looking for manga similar to Fate/Grand Order: Epic of Remnant - Ashu Tokuiten I - Akusei Kakusetsu Makyou Shinjuku - Shinjuku Genrei Jiken, you might like these titles.
In a strange twist on Arthurian legend, young Art pulls the magical sword Excalibur out of a stone--only to find himself as one of a million Arthurs, fighting to defend the island of Britain from enemies and to earn the rank of the true king. Art is pretty puny, but his childhood friend Ligu (who was also chosen by an Excalibur) tries to keep him from being immediately killed. Soon Art lives in a castle with knights, which are created beings who serve the kings. From the respect with which he treats the knights, he inspires some to hope he becomes the true king. But is that really achievable by a scrawny crybaby like him?
The continent of Yggdra is a place where humans, ogres, giants, forest sprites, and many more mythical creatures live. Led by the Holy King, the continent was at peace until one day, a mysterious group called the Black Army appeared and started conquering the land. In response, the Holy King and its troops fought against it, but Holy Capital fell and the Holy King was killed by the mysterious Black King. As the continent was in the glimpse of destruction, hope glimmered as one man, Yuri, the Hero, decided to fight back and formed the Volunteer Army to oppose the Black King and bring peace back to Yggdra