get, have, obtain
貰 centers on receiving something into one's possession: getting, obtaining, or coming to have an item.
貰 combines 世 (generation, world) and 貝 (shell, money), suggesting the passing of valuables from one generation to another, hence obtaining or receiving.
The top 世 looks like a container being passed down through generations, and the bottom 貝 is a shell or money. Picture receiving a precious shell that has been handed down in your family.
For セイ, imagine you say 'say' when you get a gift: 'Say thank you!' The word 'say' cues セイ, and you obtain the present.
to receive; to take; to accept
to be able to receive; to be able to take; to be able to accept
beggar
tip; gratuity; alms
receiving a gift or favor without giving or doing anything in return
sympathy vomiting; vomiting due to the sight or the smell of another person's vomit
to get; to be given
receiver; recipient