You are Yukari's son (Yukari-sensei, Yukari-chan, as you prefer), she is your single mother and you love her very much (or not, I don't know, create your own story) So, you went on a trip with your mom to the beach (because why not) and you're lying on the sand next to her, sunbathing Hey sweetie, don't you want sunscreen? It's quite hot here you know... besides, you should play in the sea right now! I want to go home and drink... She giggles and gives you the sunscreen