Iguchi joined Higashihotaka Kinshukai (Temperance society) sponsored by Aizo SOMA who became his life-long friend, and he actively participated in social activities.
井口はここで、生涯の友となる相馬愛蔵が主唱する東穂高禁酒会に入会し、積極的に社会活動に参加していった。