Do you like soba noodles?
Kanda Matsuya near Akihabara is a great soba restaurant with a long history. Their cold soba is very delicious and the setting of an old house is very relaxing. You can watch a soba chef making soba from your seat sometimes.
Kanda Matsuya: https://www.japantimes.co.jp/life/2006/01/06/food/kanda-matsuya-pick-your-century-of-soba/#.XaUcoef7TUI
At Komachi Shokudo, this is also in the Akihabara area, you can enjoy Shojinryori (Buddhist meal). It's very good that they serve vegan and vegetarian food as well.
Komachi Shokudo: http://konnichiha.net/komakishokudo/english.html