It's really difficult to go by just Nico Nico (I'm not as well-versed with Japanese websites as I am with Chinese) but when it comes to ARMS a lot of the focus is on the usual suspects (Helix has a bigger presence in the Japanese fanbase, it seems). There are quite a few speculation vids on Nico Nico, after all.
As for FP2, well, you're in luck. There's
this video, which is
glorious. And not just because it's 269 minutes (screenshot at 11:12) - but also because it was streamed:
View attachment 274989
I know, this is just one example (and a pretty extreme one just by length alone). It's also not the only video on this topic, as said. But still. 11 / 10 material right off the bat. And before you ask, avatars like the 3D hamburger's pretty common in Japanese streams and videos.
Timestamps if anyone is curious (Google Image Search did fail a couple times, but the character list's 99 % there):
ARMS: 20:35
Smash 4 Mii Costumes (with FP1's Costumes brought up): 52:22
Bandai Namco: 58:09 (
Tales Of at 63:45,
Digimon at 79:40,
Miscellaneous Bamco IP at 95:37.)
Spike Chunsoft: 102:22 (Mystery Dungeon: Shiren the Wanderer)
Taito: 106:28 (Yes,
Space Invaders)
Activision Blizzard: 109:50 (Tracer, Crash, CoD - Spyro's notably absent.)
Koei Tecmo: 120:50 (Hayabusa, Nioh, Dynasty Warriors, Atelier, Samurai Warriors)
From Software: 132:00 (Dark Souls, Sekiro)
Level 5: 138:15 (Layton, Inazuma Eleven, Yo-Kai Watch)
Disney: 143:16 (Sora)
Capcom: 147:38 (154:54 is where he focuses on Capcom) (Dante, Phoenix, Amaterasu, Monster Hunter, RE, he inserts Arthur and Firebrand later on)
SEGA: 167:38 (Kiryu, Arle,
Segata Sanshiro, he inserts Sakura Wars - both old-school and PS4.)
Square-Enix: 178:06 (Lara Croft, 2B, Bravely Default, Chrono Trigger, he inserts Geno about a minute or two in)
Nintendo: 183:12 (Rex + Pyra / Mythra, Karate Joe, Paper Mario, Dragalia Lost, BWD, Astral Chain, Porky,
the GBA Napoleon game (judging by the Napoleon hanafuda card) )
Pokemon Company: 196:30 (Gen 8 starters, Urshifu, Calyrex, Zarude.
No Toxicrity nor Zacian / Zamanzeta)
Characters that he didn't make specific slides for, but are visible / talked about:
Steve
Master Chief
Raiden (Metal Gear)
Doomguy
Bomberman
Reimu
Hollow Knight
Quote (Cave Story)
Cadence (CotND)
Shantae
Riki (Kunio-Kun)
(I believe FallOut? Video's capped at 360P, so it's difficult to tell.)
He comes up with several possible FP2s: 205:00, 212:50, he spends at least 15 minutes debating before going with his final FP2 at the 250 minute mark (No Spoilering because this is dedication). Mii Costume guesses at 252:58.
So yes, this dude went and ran a Smash Speculation Marathon. This was live-streamed for more than
4 hours without pause. Yes, one person - but it's undeniable proof that speculation can reach some strange heights over there too. And it's probably the most comprehensive video.