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Ruby, 70 67 bytes

f=->s{(?b..?{).each{|c|puts s if s=~/\S/;s.gsub! /[^#{c}-{]/i,' '}}

Thanks to @TuukkaX for pointing out some parens could be dropped (-3 bytes)

f.call('Hello')
 
Hello
Hello
Hello
Hello
Hello
H llo
H llo
H llo
  llo
  llo
  llo
  llo
    o
    o
    o

Ruby, 70 67 74 bytes

f=->s{puts s;(?b..?z).each{|c|s.gsub! /[^#{c}-z]/i,' ';puts s if s=~/\S/}}

Thanks to @TuukkaX for pointing out some parens could be dropped (-3 bytes)

Unfortunately I then had to add 7 bytes because original version failed to handle "z".

f.call('The quick brown fox jumps over the lazy dog!')
The quick brown fox jumps over the lazy dog!
The quick brown fox jumps over the l zy dog
The quick  rown fox jumps over the l zy dog
The qui k  rown fox jumps over the l zy dog
The qui k  rown fox jumps over the l zy  og
Th  qui k  rown fox jumps ov r th  l zy  og
Th  qui k  rown  ox jumps ov r th  l zy  og
Th  qui k  rown  ox jumps ov r th  l zy  o
T   qui k  rown  ox jumps ov r t   l zy  o
T   qu  k  rown  ox jumps ov r t   l zy  o
T   qu  k  rown  ox  umps ov r t   l zy  o
T   qu     rown  ox  umps ov r t   l zy  o
T   qu     rown  ox  umps ov r t     zy  o
T   qu     rown  ox  u ps ov r t     zy  o
T   qu     row   ox  u ps ov r t     zy  o
T   qu     r w    x  u ps  v r t     zy
T   qu     r w    x  u  s  v r t     zy
T    u     r w    x  u  s  v r t     zy
T    u       w    x  u  s  v   t     zy
T    u       w    x  u     v   t     zy
     u       w    x  u     v         zy
             w    x        v         zy
             w    x                  zy
                  x                  zy
                                     zy
                                     z

Ruby, 70 67 bytes

f=->s{(?b..?y).each{|c|puts s if s=~/\S/;s.gsub! /[^#{c}-y]/i,' '}}

Thanks to @TuukkaX for pointing out some parens could be dropped (-3 bytes)

Calling it:

f.call('Hello')

Hello
Hello
Hello
Hello
Hello
H llo
H llo
H llo
  llo
  llo
  llo
  llo
    o
    o
    o

Ruby, 70 67 bytes

f=->s{(?b..?{).each{|c|puts s if s=~/\S/;s.gsub! /[^#{c}-{]/i,' '}}

Thanks to @TuukkaX for pointing out some parens could be dropped (-3 bytes)

Calling it:

f.call('Hello')

Hello
Hello
Hello
Hello
Hello
H llo
H llo
H llo
  llo
  llo
  llo
  llo
    o
    o
    o

Ruby, 70 bytes

f=->(s){(?b..?y).each{|c|puts s if s=~/\S/;s.gsub!(/[^#{c}-y]/i,' ')}}

Calling it:

f.call('Hello')

Hello
Hello
Hello
Hello
Hello
H llo
H llo
H llo
  llo
  llo
  llo
  llo
    o
    o
    o

Ruby, 70 67 bytes

f=->s{(?b..?y).each{|c|puts s if s=~/\S/;s.gsub! /[^#{c}-y]/i,' '}}

Thanks to @TuukkaX for pointing out some parens could be dropped (-3 bytes)

Calling it:

f.call('Hello')

Hello
Hello
Hello
Hello
Hello
H llo
H llo
H llo
  llo
  llo
  llo
  llo
    o
    o
    o