Complex sentence: A significant milestone in the series that reflected this sense of hope is when QiLuo contemplated how the huge sandcastle they had built will eventually be destroyed, Ling reassured her that together, they will rebuild the sandcastle, no matter how many times it takes.
Split into simpler sentences: A significant milestone in the series reflecting this sense of hope is when Qi Luo contemplates how the huge sandcastle they had built will eventually be destroyed. Ling reassures her that they will rebuild the sandcastle together, no matter how many times it takes.