Hi Hi no Mi

The Hi Hi no Mi is a -type that allows the user to grow stronger during the day, giving them powers similar to that of the sun, thereby making them a Sun Human (太陽人間). It was eaten by Belphegor.

Etymology

 * "Hi" is the the Japanese word for "Day".
 * In the Manga and  dub it is called the Day-Day Fruit.

Strengths and Weaknesses
The first major strength of this fruit, as demonsated by Bel, is that it grants its consumer the ability to grow stronger in the day-time. All of their physical attributes are enhanced. As the day goes on, he gets stronger until noon where he is at his peak, just as the sun are is at its peak. Due to this, during the daytime, the user can produce solar energy and manipulate it, though Bel only does this to augment his martial arts, as any outward emission is taxing. Along with this, the consumer, in this case Bel, is immune to any ability or Devil Fruit that utilizes heat or light. In the case of light, he absorbs it, whereas no heat whether it is from fire or magma can harm him.

During the Timeskip, Bel having been inspired by Kevu's Regalia, and Lamorak's Syntheses wanted to create a form of his own, and came to understand that his physiology had been altered to that similar to the sun in many ways, and that he could induce a solar flare in himself which he refers to as Bagliore Solare (太陽フレア（バリオ・ソラレ）).

While this fruit is simple in nature, it has its share of weaknesses. The largest and most potent one being that when either night-time, or not directly in contact with sunlight, Bel is at his weakest, specifically at midnight. Due to this, Bel's physical state regresses to an infantile one. Despite this, he is still fully capable of moving around and talking as normal, just that his physical capabilities are greatly deminished. Blackmore Ada has come up with a way to bypass this, by creating a pacifier which stores energy from the sun. While one would think that his immunity to heat suggests that the heat produced form his solar energy is far more intense than that of magma, that is not the case. While the heat and intensity does increase as the day goes on, its level of heat only caps out to be somewhere above fire's natural state.

Aside from this, the user is succeptible to the standard Devil Fruit weaknesses.