Adabana (アダバナ) refers to any flower which doesn't bear fruit or a metaphor for something that is meaningless or fails to meet its fullest potential.
Harukanaru Toki no Naka de 6 has a different definition that is pivotal to the game's main plot. In this continuity, adabana are flowers which thrive near volcanoes and blossom with magma-red petals. They are said to grow into the true form of humanity. Within them lies enormous spiritual power. If a person is exposed to it, they can receive untold capabilities at the cost of their memories and sanity. The Demon Clan has kept tabs on the plant for ages to ensure it doesn't bring harm to others.
Seishiro obtained the flowers by deceiving Darius sometime before the main setting. The commander built a laboratory within the basement of Ryounkaku that extracts the energies within adabana. Using these inventions to draw energies from an evil god, the commander-in-chief orders for periodic experiments under the pretense of military recruitments. The young men are promised instant vigor and other lofty rewards for undergoing a "special training" program. If the recruiters are running short, they will force any young man happening to be in eyesight to take part. Viable targets are any men who looked unemployed, had no family, or who are desperate and naive.
Once a group is formed, the men are contained within an underground room and subjected to high levels of adabana gas and the evil god's curses. Immediately upon exposure, the men become violent and the room turns into a wild bloodbath. The men are expected to turn into one of the three: dead, demented or a robotic drudge. The dead have a formulated cover story of being accepted for prestigious overseas assignments.
Those who turn mad are difficult and impractical to contain, so Seishiro fabricated a lie to be spread to the Tokyo public. Anyone who is suffering the adabana's adverse side-effects is suffering from a disease which recently emerged in the imperial capital. The "sick" are dubbed tsukiyami (憑闇), the spiritually possessed who are infected by the nefarious Demon Clan. Not even the White Dragon Priestess's purification can completely save them; purified tsukiyami fall into deep comas or becoming gibbering vegetables.
His drones from the experiments are considered successes and form his personal Force Protection Squad (強兵師団, kyouhei-shidan). The public is told that these chosen soldiers protect their country using the powers of gods. Another one of their missions is to subjugate and detain the tsukiyami. Drudges are placed under the command of a sane superior with blind loyalty to Seishiro; these superiors are often the same enforcers for the experiments.
Since the deception comes from a respected authority figure and is printed into the local newspapers, the majority of the capital's residents believe it at start of the story. Though it is a military conducted travesty, not every branch of the military is aware of the truth. Either members are too intimidated by Seishiro to challenge him or trust his projected integrity enough to believe his evasion. Outsiders who get too close to the truth are silenced if they are discovered by Seishiro or his subordinates.
When members of the Force Protection Squad begin to regress into tsyukiyami in public, dissent spreads to form a group of protesters who claim they want the exploitation of gods to end. Many members of the public become afraid and begin to suspect that the bygone prophecy of the capital's annihilation may come true.