What is the function of G Major in the key of B Major

Referencing the song in context: Yoake To Hotaru

At around 3:30, the chord progression goes from Cm - Dm - EM - GM#5 - Abm from what I can see in the video.

In this case, what function does GM#5 perform in this progression, since G is not found in the key of B Major?

Unfortunately your key, chords and enharmonic spelling are inaccurate. The key is G# minor (not Ab minor) the relative minor of B. The passage can also be spelled in Ab minor but then everything else would have to change as well (C# becomes Db, etc.) The chords are actually C#m7-B/D#-Em6-D#7/Fx-G#m. Fx (double sharp) is enharmonically G.

So in answer to your question, it is not a G chord. It is actually a V chord (D#7) with the 3rd (Fx) in the bass resolving to i (G#m).

If we take your title question at face value, G does have a function in the key of B, it is the bVI chord, a borrowed chord from the parallel minor (Bm) of B. It is also referred to as modal interchange. That is not the case here though.

• I appreciate the guidance towards the correct direction. Since it's in the relative minor of B (G#m), the progression in the minor scale would be iv-III-VI-v-i, right? What makes it so that the VI becomes a minor and the v becomes a major? I've noticed that these are the equivalent of the vi and V of the G# Major scale, is there any relation to this? Jul 14, 2023 at 20:36
• The VI is vi minor for color purposes. Remember chord progressions do not have to be diatonic. If you listen about 10 seconds later a similar progression starts but that time they use the major VI, E major. It is not related to the vi in a major key because that chord would be built on the major 6th, or E#, nor E. As for the V, it is common to use a major triad or 7th chord in minor keys in order to have a V-i dominant to tonic relationship. This is the reason for the existence of the harmonic minor scale, it contains the leading tone which turns v into V. Jul 15, 2023 at 0:02