Siblings is the one hundred and fourth chapter of To Love-Ru.
Mikan gets a fever at school, but tells the teacher that she's alright. She hurries home to make dinner. When Rito and Lala get home, they find Mikan passed out on a chair arm. They put her in bed and see that her temperature is 38.2 degrees. Rito advises her to stay in bed while he and Lala do the chores. However, this is easier said than done, as Lala messes up the clothes that she was suppose to wash and Rito has a "run-in" with Mikan's bra.
Later, Rito decides to make some soup for Mikan. He brings it up to her for her to taste, only to find out by Mikan that the soup is not as good as he hoped, but Mikan still downs it, pretending it's medicine. Rito then praises Mikan for being so masterful with cooking and says that he needs her, causing her to blush. Mikan then jokes that they are not blood related while she blushes (this is a hint that she likes him, and in the anime, it is even more relevant). In the end, Lala makes a soup for her, but gives it to Zastin and the other two bodyguards. After eating it, they were on the verge of death for three days.