Lucien heard Rakuzen's words and only then did he calm down. While he was still a bit skeptical about his situation with his spirit beast, he still understood Rakuzen's words properly and found them reasonable. Unlike true spirit beast cultivators who have no other means of defending themselves without their spirit beasts, Lucien is also a mage and a capable fighter at that. Even without the spirit beast abilities, he is still a capable beast-man with the strength of two general-level magic beasts sealed in one body.
While the spirit beasts grow as his spirituality grows, he can checkmate the risk of dying by growing his mage and fighter strength and keeping everything balanced. Only after considering these things did Lucien calm down and smile.
"You don't have to worry… I am fine" Lucien suddenly said as he sat up and flexed his muscles.