I believe onikobe rin just found a way to portray wakasagihime on land in a reasonable fashion.
I remember when she was first revealed everyone was saying "How will people portray her in a manga as being with other characters? Does she only stay in the water? If she leaves will she fly around since she can't walk? How many jokes will have her flopping around like a fish out of water?".
Wakasagi-hime, make a seal impression! A seal impression!
But, seriously, if someone in fanon wants to have her walking around on land, there have been plenty of stories that have merfolk with reasons for split tails/land legs to draw from.