Lucor Fruit

Lucor Fruit (ルコルの実) is an alcoholic fruit which is extremely potent and dangerous. Its primary use is to turn one into an entire barrel of strong alcohol. It is about the size of a grape.

Overview
They appear very similar to grapes while having a bright red coloring. They are small enough to hold between your fingers and crush fairly easily. One single berry is used to make a barrel of strong alcohol which can be used to alcohol poison the water of the ocean causing fish to rise to the surface. It is very strong and just licking it will make nearly anyone dizzy, knock them out, or kill them if they were to eat it. To survive you either need to be very strong or get immediate medical treatment. It can also recover a large amount of MP and SP, for this reason Naofumi carries some to use in battle. However only Naofumi can make use of this effect due to his immunity to alcohol.

Volume 5
Naofumi started eating them thinking they were grapes. They became his favorite fruit. Motoyasu eats one, while drunk due to being interested. This leads him to pass out and get emergency help.

When Filo smells it, she runs away since she hates alcohol.

It is used during the 4th wave inside barrels of large concentrations and are exploded in the ocean. Causing the water to become highly alcoholic which makes the fish and monsters in the ocean either die or float to the surface.

During the fight with the other worlders during the 4th wave, it's used to make Glass severely drunk. Rendering her incapable of fighting. (In the manga it incapacitates L'Arc and Therese as well.)

Volume 7
Naofumi uses Lucor to replenish his MP and SP while stalling the Spirit Tortoise waiting for Fitoria to arrive.

Volume 10
Sadeena attempts to "assassinate" Naofumi using the fruit because of a hunch he would be fine. (Which happens to be correct)

Volume 14
Naofumi spiked Erhard's Master alcohol with Lucor to make him stop hitting on girls.

Trivia

 * In Japanese, the Lucor Fruit is written as 「ルコルの実」, which is a reference to how alcohol is said in Japanese 「アルコール」
 * Due to Naofumi being the only person who can eat them whole, it is often used to identify him.