I was wondering how the modulation in Sword Art Online - Swordland (Main Theme) from the Bbm in measure 19 to the Cm in measure 27.

Particularly I'm curious about why does the B chord in measure 23 work in connecting this transition? Also whether my understanding of Abm (measure 24) and Bb (25/26) is working as some type of backdoor chord progression to the Cm in measure 27, and how come using Abm and Bb chords while still in the key of Bbm still works during this transition?

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  • 1
    I upvoted you just for rephrasing the question. Commented Mar 21, 2021 at 3:13

2 Answers 2


I doesn't modulate to c minor at all. It just cuts the scene and starts up in the new key. There IS, however, a pattern to the harmonic motion.

Throughout this song, the composer frequently moves to the relative minor of the tonic major of the current minor key. (Phew!)

Before your head explodes trying to unpack that last sentence, let me just show it:

Start of song

e-minor --> c# minor (which has same key signature as E major). This is a clear (and nice) modulation to c# minor.

This passage

e♭-minor --> c minor (which has the same key signature as E♭ major)

The difference is that in the first case, they modulated TO c# minor, but in this case, they are setting up a huge cadence to stay in e-flat (VI-vi-V-???), but do a sudden fakie to ( C# ) c minor anyway.

Short version: NOT a modulation, but still a planned part of this piece's harmonic progression.

  • I'm having trouble following this analysis. How is this passage in Eb minor; if Eb minor, why is the key signature Bb minor, when the other key sig changes are explicit; and where is the sudden fake-out to C#?
    – Aaron
    Commented Mar 21, 2021 at 3:40
  • 1
    Well, it bars 23-25 are VI-iv-V in e♭ minor, and bars 25-26 are a massive pedal tone over B♭, so this is a huge cadence in E-flat. You're right about C#, it's C. That's a typo because I was thinking about the earlier section, will edit that now. Commented Mar 21, 2021 at 3:45

The overall analysis goes like this:

measure            19  20  21  22  23  24  25    26  27
chord              Bbm Gb  Db  Ab  Cb  Abm Bbsus Bb  Cm
Roman numeral Bbm: i   VI  III VII bII 
              Eb :                 bVI iv  V     V   vi

Although the modulation is to C minor, it helps to consider it in terms of Eb major. That clarifies the Bb chord as the dominant and the transition to C minor as a deceptive cadence. The Cb chord is thus clarified as a pivot chord, serving as the Neapolitan chord in Bb minor and the VI chord of Eb, borrowed from minor, along with the iv chord.

A part of what helps make this progression work is the fact that bars 23-26 are effectively in Eb minor, which is the iv relative to Bb minor. So the progression could be considered broadly as i (19-23) - iv (23-26) - vi/IV (27).

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