A year has passed since a series of ground-breaking media leaks exposed the Japan government's knowledge of and involvement in the supernatural underworld. After the initial discovery, there was chaos on a global scale, as other government programs were revealed. The human public reacted in anger and fear, resorting to violence, avoidance and outright denial. As for the supernatural, some relished the opportunity to exist in the open, while others went into hiding to avoid retribution. To control the situation, strict national curfews were enforced at dusk and military units were deployed to keep the peace. In the summer of 2013, the chaos has settled and curfews are revoked, though humans and demons still struggle to adjust.
Along with knowledge of supernatural creatures came a public understanding that mystical convergences, Hellmouths and even portals to other worlds are real, like the one exists in Tokyo, Japan. It first opened on September 24, 2009 at 10:21pm, in 'Community Area 11', also known as Ueno Park. The portal opened unto an unknown dimension. The breech lasted only seconds, but the effects were extensive. A mysterious type of energy briefly radiated from the portal, severely mutating some of the residents. As a result, Ueno Park underwent a mandatory evacuation. All uninjured residents were rescued. The wounded that could be captured were removed to quarantine; it was later determined that the effects on victims were permanent, but not a bio-threat.
Military presence remained around Ueno Park. Their rationale was to protect the population from a repeat of the event. At first, only barbed wire and sandbags separated it from the rest of the city. Within a month, a wall was erected around the community perimeter and armed guards were stationed there. All access points to and from Ueno Park were blocked (including access by water), except one... An undiscovered freight tunnel, no longer on the city plans.
As for the portal, it remains active. At intervals it opens long enough to expel a person, creature, object, or influential energy from another dimension. The portal doesn't open to one specific universe. It wobbles, opening to a variety of heavens, hells and alternate universes, or even time periods, completely at random. The portal also shifts, never opening in a predictable spot in the city, though it most frequently opens near Ueno Park. When it opens, there are localized electromagnetic disturbances. Knowledge of the original portal is widespread, but its unpredictable nature has led to some confusion over whether the repeat occurrences are the same phenomenon or not (they are).
Heroes and villains have begun to relocate to Tokyo, either in hopes of subduing the portal's periodic effects, or to exploit the situation to their liking.