He draws in the details in an effort to distract himself from his own pain and loneliness, which is an old wound, old grief. He was worried more for Wei Wuxian than he isn't comparable to his own, but deep down, he knows, that while the both of them are similar, like soultwins, he also knows that the both of them are different.

Quietly, "You may add lotus pods. Just like yourself, he loves to eat lotus seeds, either out of it or as candy."

Eventually, the picture is being drawn out and taken shape. Even though Lan Zhan is in pain, this is a picture that he and Wei Ying draw together to fill in the colors, the details, that to Lan Zhan, the picture itself holds special energy, like putting in their heart and soul into the picture.

As the picture is almost finished and it looks like a portrait, rich in details and color, while he is hurting and missing him. Lan Wangji felt the care and warmth that this one has for him.

So turning to him with gratitude, "Wei Wuxian, thank you. You may not realize it, but you saved me."