Chapitre 1122: Chapter 1042: Each their progress

While Maria, Luna, Sakuya, and Gracier participated in an auction to acquire elixirs and other items to enhance their mana pool, in other locations as well the remaining girls did the same, they acquired various elixirs and items not only to enhance their mana pool but to increase other stats as well. 

It is true that as one would progress one's stats would increase as well but only relying on your natural level-up benefits would not work because others might be blessed to stumble upon elixirs, items to increase their stats, it is why those high-level rankers would buy elixirs and enhancement items as their level and Rank increase. A perfect acknowledgment by your Gift could also increase some random stats after you passed a test handed by your Gift. 

It was exactly what happened to Sera, she consumed elixirs but was not satisfied with the results and therefore sought the complete acknowledgment of her Gift and he gave her a mission.