Edit in JSFiddle

<h2>
align-self
</h2>
※align-itemsにはflex-startを指定。
<h3>
auto(初期値。align-itemsの値を継承。)
</h3>
<div class="wrapper auto">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

<h3>
stretch
</h3>
<div class="wrapper stretch">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

<h3>
flex-start
</h3>
<div class="wrapper flex-start">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

<h3>
flex-end
</h3>
<div class="wrapper flex-end">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

<h3>
center
</h3>
<div class="wrapper center">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

<h3>
baseline
</h3>
<div class="wrapper baseline">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

body {
  padding: 20px;
  padding-bottom:100px;
  font-family: Helvetica;
}

.wrapper {
  display: flex;
  background-color:#eee;
  margin-bottom:10px;
  border:1px solid #CCC;
  height:150px;
  align-items:flex-start;
 
}

.auto > .box {
    align-self: auto;
}
.stretch > .box {
    align-self: stretch;
}
.flex-end > .box {
    align-self: flex-end;
}
.center > .box {
    align-self: center;
}
.baseline {
  .box {
    align-self: baseline;
  }
  
  .a {
    height:70px;
  }
  
  .b {
    font-size:3rem;
  }
  
  .c {
    font-size:0.5rem;
    padding:1rem;
  }
  
}


.box {
  background-color: #20262e;
  color: #fff;
  border-radius: 3px;
  padding: 20px;
  margin:10px;
  font-size: 14px;
}