user-1: About a week or two ago I realized that Love Live's school idol music NEVER uses the diminished chord out of the seven diatonic chords in a key.
In major keys, the diatonic chords are: 

I / ii / iii / IV / V / vi / viio

And in minor keys:

i / iio / III / iv / v / VI / VII

But the thing here is, that neither the viio chord in major keys nor the iio in minor is used in Love Live's music.  In minor keys, sometimes even that v chord is used.  Love Live tends to use both major and minor keys, and uses all of the diatonic chords EXCEPT for the viio and iio.  
For example, in this song in D minor, I hear:

Dm, F, Gm, A, Bb, C (i, III, iv, V, VI, VII)

But I cannot find Edim (iio) ANYWHERE in the song.
Also in Aishiteru Banzai,, you could definitely see E, F#m, G#m, A, B, C#m, but there is no D#dim AT ALL.
Now I am curious about is there a particular reason why Love Live does not use the diminished diatonic chord.  Will my question be on-topic if I post it on A&M?

user1458: No, this would not be on topic on A&M.
This question would not be about Anime or Manga as defined in the scope in the help center, as it is not about Anime or Manga, but about musical analysis.

user63: Music theory is most certainly not on-topic. 
Progressions using 
vii∘ (I–IV–vii∘–I and I–ii–vii∘–I) are less common because of the instability of diminished chords. The diminished tone dilemma you pose is encapsulated in this question on music.se.

-1: <p>About a week or two ago I realized that Love Live's school idol music NEVER uses the diminished chord out of the seven <a href="https://en.wikipedia.org/wiki/Function_(music)#Viennese_theory_of_the_degrees" rel="nofollow noreferrer">diatonic chords</a> in a key.</p>

<p>In major keys, the diatonic chords are: </p>

<blockquote>
  <p>I / ii / iii / IV / V / vi / vii<sup>o</sup></p>
</blockquote>

<p>And in minor keys:</p>

<blockquote>
  <p>i / ii<sup>o</sup> / III / iv / v / VI / VII</p>
</blockquote>

<p>But the thing here is, that neither the vii<sup>o</sup> chord in major keys nor the ii<sup>o</sup> in minor is used in Love Live's music.  In minor keys, sometimes even that v chord is used.  Love Live tends to use both major and minor keys, and uses all of the diatonic chords EXCEPT for the vii<sup>o</sup> and ii<sup>o</sup>.  </p>

<p>For example, in <a href="https://www.youtube.com/watch?v=LUvNP_BsU6E" rel="nofollow noreferrer">this song</a> in D minor, I hear:</p>

<blockquote>
  <p>Dm, F, Gm, A, Bb, C (i, III, iv, V, VI, VII)</p>
</blockquote>

<p>But I cannot find Edim (ii<sup>o</sup>) ANYWHERE in the song.</p>

<p>Also in <a href="https://tabs.ultimate-guitar.com/tab/misc-cartoons/love-live-school-idol-project-aishiteru-banzai-chords-1502626" rel="nofollow noreferrer"><em>Aishiteru Banzai</em>,</a>, you could definitely see E, F#m, G#m, A, B, C#m, but <strong>there is no D#dim AT ALL.</strong></p>

<p>Now I am curious about is there a particular reason why Love Live does not use the diminished diatonic chord.  Will my question be on-topic if I post it on A&amp;M?</p>
 1458: <p>No, this would not be on topic on A&amp;M.</p>

<p>This question would not be about Anime or Manga as defined in the scope in the <a href="https://anime.stackexchange.com/help">help center</a>, as it is not about Anime or Manga, but about musical analysis.</p>
 63: <p>Music theory is most certainly not on-topic. </p>

<p>Progressions using 
vii∘ (I–IV–vii∘–I and I–ii–vii∘–I) are less common because of the instability of diminished chords. The diminished tone dilemma you pose is encapsulated in <a href="https://music.stackexchange.com/questions/79438/are-the-diminished-chords-not-that-common-in-modern-popular-music">this question</a> on music.se.</p>
