Fusion

Fusion is technique which the Light quadruplets have been practicing since they were first formed. It is the process of two or more minds fusing to become one, essentially becoming a pure hivemind. They have even practiced the ability when seperated into 4 different bodies.

Description
The four minds, or two or three, depending on how many are fused at once, can switch between being active, or in the background. When in one body, they can do it at will, while in seperate bodies, they must physically contact each other to be able to fuse into one body. A mind is said to be active, or conscious, when they are present and speaking or preforming actions. They are said to be in the background, or unconscious, when they aren't presently paying full attention to their surroundings, kind of like sleeping.

When in different bodies, fusion can be preformed by physically contacting the other, or others, and consciously thinking about fusing with each other. Light and Licht were toe first to attempt to, and succeed in fusing for the first time, in seperate bodies. This causes the ones fusing to revert to a state where they are both physically in one body, sort of like Tito was before the Vox incident.

When in one body, after a successful physical fusion, or before the four had seperated, a fusion causes the two, or three or four, minds to be linked in a hivemind state. They are all consciouslly aware to an extent, and have a similar train of thought (which is typically how this is triggered).

Outcomes of Fusing
If two minds are fused, physically or mentally, then there is no harm that can come to the two, and the fusion can go on indefinitly. When three minds are fuse mentally, the minds tend to be more rash in decisions, mostly because of the absence of the fourth mind. Physically the body is taxed more, having to accomodate 4 bodies having physically and mentally linked. If and when all four minds are fused together, mentally Tito is said to be at his fullest potential being able to think as all four minds at once, and giving him a much better feeling of everything happening around him, thanks to Hikari. At the same time his body greatly stressed, since the four mind's seperate bodies have grown acustom to living independently of one another. Hikari even states "We [Tito] may even end up in a coma from energy loss." She is openly admitting that fusing together fully, after having seperated, would cause a great strain on the body, albeit being able to use all four powers at the sam time, and is best advised to be avoided.