Some Re:Zero fanfic ideas, crossover mostly

Big Sonic 2: General Sonic world stuff:

Changes that apply no matter where in the timeline you take him from: Different geography, with several real locations having analogues like Empire City for New York and United Federation for USA, but others such as Japan keeping their regular names(mentioned by name in Shadow the Hedgehog, never visited). There are a lot of islands, including some that move around and some floating land masses are known about(most of the public seems to not believe at least Angel Island at first). Lots of contemporary tech cityscapes exist on several of these islands and the mainland that include stuff such as skyscrapers. Little Planet appears for 1 month each year above Never Lake and is a popular tourist attraction, Time Stones are probably known to the public at least in legend. There are also just random floating platforms around the place. Floating golden rings exist all around the planet, in space, and even on other planets, they can be used as a power source for machines and non-machines(ring energy)(Sonic Rivals 2: Silver needed rings to recharge ESP, Knuckles for emerald detector radar device, there is an area in that game where rings reappear within 20 sec of being collected), and are used as currency, an inventory system or tech to store them?(An apple costs 30 rings in Sonic Unleashed)(Unsure if rings protecting from damage property is cannon or only something for the main cast, it shows up in Prime and a Frontiers cutscene). Loop-de-loops are a regular part of the environment, with there both being natural forming ones and manmade ones being part of highways and whatnot in some areas for some reason, along with natural checkerboard patterned soil in many places. Some areas are extremely cartoony, such as Music Plant and Toy Kingdom(unsure how natural they are, music plant definitely has things like tunnels of brass instruments). (A second moon is seen at the same time as the moon in the Chaos Angel and Crimson Crater backgrounds, so random planetoid similar to Little Planet exists? Never mentioned directly.)

Anthropomorphic animal people exist, humans are more common on the mainland, Anthros are more common on the islands. Several antros have powers, whether they be species-wide or for the individual, with a very small number of humans also having some sort of power, unsure what the average strength of humans is(Eggman is a power type in the riders games and continuously manhandles whoever in the IDW comics), probably keep Subaru at his cannon strength(Don't think any fantasy races such as Elves exist, but the idea of them seems to exist). Some more extreme wild animals exist such as multiple different giant snakes, giant frogs that can summon the rain, very small and cute Dragons(SA2), Chao, a Phoenix that acts as the Chun-nan Gia Temple's protector, etc. (Temperament would probably be considered just standard wild animals mostly). Some sort of magic exists among some part of the population, based on Amy's Tarot cards and ability to go invisible, Witchcart's ability to magically shoot beams that encase things in crystal with a magic wand(Tails 30th anniversary IDW comic), and Mystic Melody. Ghosts seem to exist, but only in certain areas, probably known to the public because some areas with constant supernatural activity are completely accessible to the public, such as Pumpkin Hill, which is very close to Central City(the fact that Ghosts can be trapped in Robotnik capsules is probably not known).

Tech is far more advanced in some areas including a city with flying cars and whatnot called Monopole from the Sonic Riders game(name only in Japanese version) and a lot of other futuristic cities. A piece of tech that is relatively common in some areas is extreme gear, with some types being hoverboards, hover skates, and hover bikes(Can give Subaru one of these if you feel like it, Sonic Riders-style outfit Subaru?). A lot of randos just happen to have non-extreme gear hover vehicles and whatnot, such as Fang the Hunter, the Whitchcarters, and Amy. Security robots are common in some areas such as casinos, some of which have been sold by eggman(Some point before Battle forward?). GUN robots run off of chaos drives, but unsure how chaos drives would be available to the public(Unless salvage, possibly post-forces if so)(Also, GUN's existence and their tech, much of the tech came into existence 50 years before SA2). So many ancient civilizations, many of which were technically advanced. Unsure how some level-up items would work for characters outside of the main cast such as the Bounce Bracelet, but others such as the Air Necklace, treasure gage, and sunglasses would probably work for anyone.(Invisible rings, item boxes, and springs that can only be interacted with when they are seen using the latter two level-up items also exists in Sonic's world I guess, one could be what he tries to sell at the start of the series) I guess people put springs and item boxes everywhere(poster for Spring festival and item box expo in city escape) I am unsure about some items included in item monitors such as shields and invincibility.

IDW comics state that the heroes and villains are only the current generation, so there were heroes and villains before them(writer said Vanilla, Cream's mom, might have been one of the adventuring heroes). Stand-ins for any mention of God, such as Gia or Solaris. Movies and other stuff are largely different with some examples being Chao in Space, Planet Of the Chaos, Chaos soda, and ChaOS.(Lego seems to exist regularly, based on TailesTube desktop)(Pretty sure language is the same as real life in Sonic world) (Unsure how close to public knowledge info about the Chaos Emeralds are at the start, but they definitely are public knowledge Adventure forward, think that Special Stages would not be known outside of vague rumors or legends, unless some rando wandered through a Big Ring in a city stage in Mania or something)