It has been established in HEAVENS that nobody should ever argue in front of Nagi or Shion.
The rule was first implemented for Nagi’s sake, during the times when HEAVENS was just a three-person band. In the past, Eiichi and Kira did not see eye to eye. Arguments ranging from bickers to yells would erupt. At those times, Nagi treated it as a mere nuisance and shrugged it off, assuming it’d blow over. However, a terrible fight between Eiichi and Kira began and lasted four days with Nagi being there to witness each one. It was caused by HEAVENS loss against STARISH, since the fault seemed to be their lack of ability. By the fourth day, Nagi broke down, overwhelmed by the unending arguments, having no one to talk about his feelings to.
At that moment, Eiichi realized that for HEAVENS to become stronger, they have to work together and start caring for each other. Eiichi and Kira then put aside their problems, and decide to be more responsible around Nagi by avoiding arguments whenever the child was present.
When HEAVENS turned into a seven-man band, the arguments had lessened to little spats, big fights becoming almost obsolete, until one day, the news that Yamato assaulted Syo reached them.
Eiichi scolded Yamato, but the latter was stubborn and fought back. Soon, they began yelling. Kira and Eiji immediately tried to escort Nagi away from the scene, but they had not accounted for Shion.
Just as Yamato looked like he’d take a swing at Eiichi, Shion threw himself in between them, begging them to stop. It was his first time seeing an serious argument between his friends, and he was already in tears. After that, he just ran into the closet, locking himself away.
Shion refused to come out, but he opened the door when Nagi asked to join him, because he too felt like he needed some quiet time. After chatting about their feelings, Shion was ready to leave the closet.
Ever since that day, the rest of HEAVENS swore to never argue in front of Shion and/or Nagi again, because no good ever came out of it.