Sooner or later, many long-running Japanese music game series tend to reach a certain limit on how an hard chart for certain songs can be molded into for the difficulty standards of their original inception and when something like this happens, a new and harder layer of extra challenge in form of an additional difficulty may spring up for selected songs to spice things up by keeping older tracks up-to-date with the always-evolving difficulty meta.
For the Taiko no Tatsujin series, the Ura Oni modes is filling this peculiar slot for a long time, but how is this concept translated into other series? Step in to get a taste of what breaking a chart's limits feels like in other renowned rhythm games! For chart comparisons, we're also leaving the former-harder difficulty below each of the featured videos.
Regular EX video
Stating off with a quite curious trivia, did you know that Taiko no Tatsujin isn't the first music game to make usage of actually-labeled Ura modes? In fact, that merit goes to the pop'n music series, as its 11th installment in 2004 (and related PS2 port) has added harder Ura charts to some of the older songs, becoming (so far) the only entry in the series to proposing an alternative difficulty set to the standard modes (5-button, Normal, Hard and EX).
The song shown above is Kiyotaka 'Simonman' Sugimoto (杉本清隆)'s Nishishinjuku Seisou Kyoku (lit. 'Nisei Cleaning Song'), from pop'n music 5. Like the other Ura songs, this one comes with the addition of the 'URA' bit as part of the song's genre relocation and its rival character is shown in its P3 color scheme. Watch out for those jacks during the speed-up!
Regular Expert video
Way earlier than pop'n, however, is the introduction of a mode in the DanceDanceRevolution series that has often hosted harder chart variants since the PlayStation port of the year 2000's DDR 4th Mix. This is Challenge mode, a feature that tests the player's skills in either pre-existing or exclusive tracks/song remixes while playing with different conditions, such as forced modifiers or with point milestones to reach in order to be cleared.
As time went by and Challenge mode was added into the arcade family, it soon became the home for harder charts of pre-existing/newcomer songs, such is the case of AWAKE by Yasuhiro 'TAG' Taguchi (田口康裕) and Rio Hiiragi (柊木りお).
The extra difficulty history for the beatmania IIDX franchise has had a different development among the years, of which we're going to talk about with a double song feature for both console and arcade fronts.
Originally started as a console-exclusive feature, an harder challenge layer for selected songs under the name of 黒Another (lit. 'Black Another') was added for the PlayStation 2 console ports of the 15th and 16th installments (DJ TROOPERS and EMPRESS) as hidden unlockables to be unveiled through cheat code magic. With the console front being dormant for a long time (at least until the recent release of the subscription-based IIDX INFINITAS for PC), harder charts for pre-existing songs started to be a recurring arcade feature only from the 21st main release (IIDX 21 SPADA), with the introduction of the LEGGENDARIA charts (Italian word for 'Legendary', often added in song titles as the '†' cross).
Above we can have a taste of both worlds, with Yoshitaka Nishimura's MENDES from IIDX 15 in a double-play video as one of the greatest Black Another representatives (chart on the right, regular Another on the left), currently being the one challenge with the highest notecount of anything IIDX-related! For a more modern spin, there's the recently-released † chart for Maozon's Damage Per Second from IIDX 23 copula, which also integrates the later-added Hold-me notes gimmick.
Regular Extreme video
A quick mention to jubeat is in order, as the coming of 2014's main arcade entry -jubeat prop- has added a new kind of note markers in Hold notes, welcoming this addition by featuring the  difficulty set for some of the pre-existing songs in order to update their charts with the new kind of note while still keeping the original sets.
Up here is a song that really needs no introduction, considering the many travels it has done in rhythm gaming so far...
Similar to DanceDanceRevolution's Challenge mode, the later-released REFLEC BEAT series also has a peculiar game mode where songs may become harder not only for notechart changes, dubbed the Special mode. Released in 2014 for REFLEC BEAT groovin'!!, all Special charts had to be unlocked by in-game performance currency after fulfilling certain conditions.
Sung by Selen Kusonoki, up here we have composer Hige Driver's Dadadadadadadadadada (打打打打打打打打打打) in its harder form yet. And yes, that song title is still as real as it's ridiculous!
The song submission-driven SOUND VOLTEX series is also keen on extra difficulty shenanigans, with the major distinctive flair being said additional mode being named differently for each release, according to said arcade's title; to give out some examples, this extra mode in its debut game -SDVX II infinite infection- is called INFINITE, while in the the sequel, GRAVITY WARS, they're labeled as GRAVITY charts. All these extra modes follow the DDR and RB scheme in that they might be something more/different than just new chart challenges such as modifier forcing or other visual flairs of different nature.
Among the EXIT TUNES licenses we can find Cosmo@BousouP's XyHATTE, whose title is read as the Japanese word Saihatte (最果て, lit. 'Farthest'). How far can your eyes go with this improved chart?
For our last bemani-related stop in this feature (I swear), here's a one-of-a-kind boss chart from BeatStream, one of the most recent franchises! When it comes to extra modes, NIGHTMARE charts play as harder difficulty variants of BEAST, being rated in a numbered scale. That's the usual norm...
...but for composer Tatsuya 'Qrispy Joybox' Iyama (伊山達也)'s CHERNOBOG, its NIGHTMARE chart was deemed too brutal to warrant its own god-like Kami (神) rating instead of a numerical rating! May the Slavic deities be with whoever wants to challenge the highest chaos.
For Sega's maimai arcades, the idea of a mode that goes beyond the regular Master mode is conceived as something that is done as a reply to the original Master mode; thus, the naming of Re:Master was born!
One of the latest Re:Master features was made for the Sonic Generations remix of Sonic Adventure 2's City Escape BGM, arranged by Cash Cash. Follow those sliders as a gameplay video is played it the center!
Instead of single extra modes for pre-existing songs, Sega's CHUNITHM games has its own dedicated mode where both limited songs and permanently-available charts with more taxing difficulties are grouped together to be selected and rated in a different rating scale from the usual number system. That's the magnitude of the WORLD'S END mode to you!
The WORLD'S END notechart variant we're spotlighting above is the one for Sampling Masters MEGA's The wheel to the right (which we've also talked about in the past) as a means to see the mode's more gimmicky side: as suggested by the song's title, in fact, all of the notes that have to be hit are placed on the right half of the playing field, limiting the hand movement of the players from the usual full-field feel!
One look at Taito's Music GunGun! series is enough to see that some other franchises can reserve their extra difficulty sauce for licensed/other sourced tracks, just like Taiko no Tatsujin! Up here, for example, is the Very Hard mode for the original Hatsune Miku no Shoushitsu, one of the two Vocaloid songs in the game to warrant the Very Hard treatment.
For another look at 'licensed enhancements' under Taito management, here's an example from the Groove Coaster series's EXTRA mode formula, here applied to REDALiCE's Colors, one of the very first Touhou Project arrangements to reach out the series.
As you can hear, the Extra mode features a different keysound setting that relies more on percussions, while bringing along an harder playable challenge!
This is the end of our brief tour though difficulty enhancements. Take care!