Cafe Seiren is a common meeting place for members of the cast to gather for social outings. Events of both the main storyline and various side stories take place within it. It is also possible to visit the cafe at will, where Itsuki can order an item from either the food or drink menu to restore the party's health and give luck boosts to individual party members.
The waitress that serves Itsuki when he visits Cafe Seiren for food or drink resemblesof Fire Emblem: Path of Radiance and Radiant Dawn. The waitress offers side quests to Itsuki that consist of bringing her ingredients for experimental new menu items. When the side quests are completed, the new items are added to the menu and can be ordered like the standard menu items.
- Cafe Seiren is named after the translation-literal way of reading Siren (セイレーン, Seirēn)? in Japanese, minus the macron E. This is a nod to how Starbucks's logo is based on a two tailed siren.
- The demon that makes up the logo of Cafe Seiren, on the other hand is Mermaid, as the demon Siren largely is based on her avian depictions from the original Greek myths, before their image got conflated with Mermaid's.
- The real world location of Cafe Seiren is the Starbucks Shibuya Tsutaya, located at the famous Shibuya Crossing in Tokyo.