Famitsu has published another article about Exstetra with a few more screenshots and details. You can find the images and a summary of information below – translation courtesy of Siliconera.

Recap

– Game’s premise is Tokyo having fused with the alternate world Amasia
– Ryoma, an amnesiac student, learns that your kiss turns others into Prisma Knights
– This affects both men and women
– Sword-wielding Jin and archer Mizuki will team up with Ryoma
– Ryoma’s powers mark him as the Prisma, the messiah destined to save Amasia from its destruction and return worlds to normality

New details

– The area around Tokyo’s Akihabara has now fallen as silent as the grave
– Area has buildings and bridges adorn with lush tropical greens
– Delving into Akihabara’s dungeon, it spreads off as far as the eye can see, bleak darkness with shafts of light punctuating its metallic corridors and walkways
– Impossible drops and far off pillars make for difficult traveling
– Ryoma and friends will retire to Seiba village in between exploring Tokyo
– Depending on how the various heroines are feeling, special side interaction events between Ryoma and the girls could be unlocked

Source