I would like to recommend a doujin game of fate here. Although I have never played fate series including FGO before, I find this game very attractive. The game is called "Fate/Empire of Dirt". It's still in progress and is scheduled for sale on C94 or C95. But you can download demo from developer`s twitter. There will be 6 servant (4 females and 2 males) in full version. In this game, some servants' twisted mind will become dungeons, and you will be exploring these dungeons, solving puzzles and ultimately defeating them to give them relief. I love this type of story, plus this game has a good script! In addition, this game's bgm sounds wonderful. Battle adopts a similar system as in FGO. For more details, please download the demo and have a try yourself.
Here's developer`s twitter, please find demo's download address at the page top: https://twitter.com/maple_LuwenWS Demo version has only Japanese language