Some Re:Zero fanfic ideas, crossover mostly

Re:Zero X Puyo Puyo ideas

Crack Idea: Subaru lived in Suzuran and enjoyed Puyo Battling pre-summoning. In this, Puyo exist around the Re:Zero world, but there hasn't been much development with them thanks to them being quite benign and the lack of any apparent use for them until Subaru's arrival(or they start falling from the sky with Subaru's arrival).

Warning: Some Puyo Puyo spoilers. 

Puyo Battles canonically work because popping Puyo by putting 4+ in a row gives one mana(incantation:'Owanimo'), so as long as one keeps popping Puyo,they have effectively unlimited mana(similar with clearing Tetriminos). Also, the Puyo are sent to some other dimension when popped, so those doing this are occasionally randomly transported to places. Puyo popping for a casual spell from a Drama CD(The spells can be done without Puyo popping, it just uses whatever mana the caster has on them like normal magic). Puyo popping seems to be invisible to third parties, so it just looks like those doing the popping are just spamming spells, probably accompanied by Puyo dropping/popping sound effects? Note: "In the case that you have a partner in battle and manage to perfectly match your timing with theirs, your chains will synchronize with one another and produce a tremendous amount of energy, unmatched by what can be achieved under regular conditions."-Drama CD

The unnamed world that Suzuran exists in seems to be just Earth(except 1+animal people because of an experiment(cartoony circumstances), an absurdly good train system, and anime color hair) until Puyo Puyo 7, in which a number of Puyo start raining down on Suzuran briefly, accompanied with a mysterious light that allows those exposed to pop Puyo(Unsure what this did, potentially modified his gate to be more stable and/or compatible with Puyo Puyo magic/Madou Monogatari magic/'Owanimo'?(incorporating Re:Zero gate idea into this)). For the sake of setting up a scenario, let's say that this happened in 2009 because that was when Puyo Puyo 7 was released and Subaru was isekai'd in 2014 because that's when the first volume of the light novel was released(ignoring the web novel), Isekai'd to Re:Zero at 17 years old, so he's around 12 when Puyo happens(time spans can be changed very easily). At 12, Puyo becoming available as a thing you could do would intersect with his early Junior High(probably at Suzuran Junior High for this), so we have him learning that he isn't a child prodigy while also happening to gain the ability to use magic by playing a puzzle game. He wouldn't get as much attention thanks to all the Puyo shenanigans and Risukuma accidentally blowing up the Science clubroom and changing his appearance, also accidently, in the process(3 months before Puyo Puyo 7). At the very least, he could get into some relatively minor shenanigans with magic, probably noticed by Ecolo if Subaru can remember him(probably can)? Maybe no one or almost no one at high school being able to pop Puyo could be the cause of his depression(if it happens) or people avoiding him because of being freaked out by magic? Also, a large part of the events of Puyo Puyo Tetris + 2 happen with him in the area, but are forgotten because of plot. 

Could keep him in Kenichi's shadow or for this sudden appearance of Puyo gives Subaru a new opportunity to get out of his shadow(or all of the events involving Puyo/Puyo characters that simply don't involve his dad could lead to this). With the second option, could also have him get Isekai'd 1 + times previous to the regular start of the story thanks to the dimension warping properties of Puyo battling, and therefore being much more level headed when getting to the Re:Zero world(and also having a possible way home), especially if he runs into one like Ragnus(Reflection of a mindset similar to an isekai mindset). (Note: Puyo transportation tends to cause those transported to fall from the sky). 1st isekai could be to a pre-established Puyo Puyo world where he could get more advanced magic?(Or he doesn't know magic pre-first transportation and just puts mana into his physical attacks before then. Also, an option is for the better gate thing to be caused by him being given some magic thing, Raffina's pouch is some kind of magic amplifier.)(If Isekai'd to Primp Town, extra info about the surrounding area in Puyo Puyo Quest's story and some translated extras from Puyo Puyo Fever 2)(Note about the possibility of just being transported to Outer Space and being stuck for a bit)(With the multiple isekai option, could have it start at the Puyo incident and go on or not)There's also the option of him learning magic from random Puyo characters that were in Suzuran with or without any isekai from his end until Re:Zero as they tend to do and/or come up with some on his own. (Accord was randomly in Suzuran during Puyo Puyo Tetris, so could be there at other times)He could also have some Puyo-themed design on his clothes or a little Puyo-themed accessory. Potential situation with learning magic pre-summoning: One option is for him to just learn Re:Zero Yin type spells, another is just learning Re:Zero spells of different affinities(could add some stuff with curses/curse detection into this). A third option is for him to copy spells from various characters that he encountered or make spells in a similar vein to those spells, whether they are imitations or, from his perspective, original(last one if he doesn't see anyone use magic, Ringo was able to make up her own magic)Also, could also know some non-combat spells such as the anti-aging stuff Accord and Lemres use or Lemres's candy-summoning spell. Could also add some martial arts in there or have him use techniques that are more weaponizing a toy more than anything similar to how Maguro fights(or Ringo's "spell" that is her bashing in an opponent's head with a math textbook, which somehow uses mana. Flow method for these?). If Isekai'd to Primp Town at some point, he could take pictures of the instructions on how to do interesting-looking spells in the library?