At simply 22 years old, Souichi already holds important status in Terra as the lieutenant commander; the second in command. He's the one that stands in for Kunugi whenever he's absent. Though easy going and friendly, Yagumo takes his job very seriously and never lets anyone act sloely on their emotions. This is especially evident when he has arguments with Elvy Hadhiyadt acting on hatred towards Ayato when she finds out that Ayato is a Mulian; Souichiro is one of the few characters who encourages Ayato to accept himself for who is, not for his genetic makeup.
Yagumo holds a secret relationship with Kim Hotal and the two looked to have a bright future together. Unfortunately, it all comes to an end when he's killed by RahXephon-Ayato on the last episode. However, it is strongly hinted that he could very well be alive in the world after the tuning.