"Fujiwara, I want to ask you something."
Hara Kei didn't respond to her previous words; instead, he began questioning her directly. "One of your parents… they must go to the hospital fairly often, right? Pretty regularly. Let me think… maybe every six months?"
"Eh?" Chika's eyes widened in surprise. "H-Hara Kei… how do you know that? My mother does go to the hospital every six months. According to my dad, she has a very rare condition that requires regular check-ups. Dad even jokingly called her the 'Glass Beauty,' and somehow ended up bruising his own back in the process."
"…That aside," Hara Kei shook his head at what he mentally labeled as her father's idiocy, continuing, "your mother probably can't cook, doesn't do illustrations, and in daily life follows a 'safety first' principle, avoiding all possible risks. She doesn't even like being around pets. Am I right?"
"That's true," Chika admitted, recalling. "When we got Pes, my mother seemed really resistant, claiming she was allergic to fur. But I knew that was just an excuse—she has so many fur coats. In the end, she couldn't resist our pleading, so she gave in…" Chika's expression softened in memory. "Hara Kei, how do you know all this?" Her gaze grew steadily more curious. "Do you know my mother personally?"
"No way. How could I ever come into contact with someone like her?" Hara Kei shook his head, then rested his chin in his hand, pretending to ponder. "But… I think I understand now."
Understand what? Could it be? Chika's previously cold heart seemed to stir with a flicker of life. She stared at Hara Kei's profile, her gaze so intense it felt like it could burn his cheek.
Hara Kei didn't keep her waiting. "Fujiwara, you asked me before, right? 'If both parents are type O, how could they have a type A daughter?'"
Chika was too nervous to speak and could only nod without hesitation. Hara Kei's words had reignited a glimmer of hope in her heart. Could it be…?
"Normally speaking, two type O parents cannot produce a type A daughter. Mendel's laws of inheritance are not wrong."
The light in Chika's eyes dimmed rapidly.
"The error lies in the testing."
"Eh?"
"No, that's not quite right. It's better to say the AB blood type test can't detect your mother's true blood type."
"???" Question marks seemed to explode above Chika's head.
"Fujiwara, have you ever heard of the 'Bombay blood type' or what's sometimes called 'pseudo-O'?"
"'Pseudo-O'?!" Chika didn't know what the Bombay blood type was, but the second term was easy enough to understand.
"Exactly. The Bombay blood type is extremely rare, first discovered in Mumbai, hence the name." Hara Kei's knowledge came naturally from his system panel.
Through his game-like system interface, Hara Kei's studying counted as 'effort.' Effort always yields results—though not in a linear fashion. Unfortunately, the system didn't categorize subjects like literature, math, or biology separately; it bundled them into a single skill called High School Knowledge, with only English and Cooking as exceptions.
Without a doubt, Hara Kei had spent more effort leveling up High School Knowledge than Piano, and the skill had long since reached Lv3, making him a proud "high-ability user."
Like Piano, however, High School Knowledge had stalled; its progress bar climbed slower than a snail. Hara Kei had several hypotheses about the situation, but they were irrelevant for the moment. Human life took precedence.
"Because of a genetic defect, people with the Bombay blood type cannot produce A or B antigens on their red blood cells, regardless of whether they carry the A or B alleles. They cannot receive blood of any AB type."
"This trait is very similar to type O blood, so modern blood tests often mistakenly identify Bombay blood as O blood. Hence the name 'pseudo-O.'"
"Fujiwara, based on what you've told me, I think your mother likely has this extremely rare Bombay blood type. That's the so-called 'very rare condition.'"
"…Going to the hospital twice a year?"
"People with Bombay blood type have agglutination reactions to most other blood types, so special blood bank reserves are necessary." Hara Kei explained. "Your mother goes regularly to have her blood drawn. Every six months is probably due to blood storage limits."
"So… 'doesn't do housework, avoids pets'… oh, I get it. Afraid of getting hurt?" Chika asked, then realized it herself mid-sentence.
Hara Kei nodded. "Even with a dedicated blood bank, the supply isn't infinite. If she were injured too often in a short period, she'd run out… you understand what I mean, right?"
Chika did.
"…The Bombay blood type… is it common?" After a pause, she asked quietly.
"No." Hara Kei answered immediately, still calm, as though he hadn't noticed the hope in her voice. "Even in Mumbai, it accounts for only one in ten thousand. European researchers estimate one in a million. Sakurajima doesn't have data, but even with optimistic calculations, it's unlikely to exceed one in ten thousand."
"One in ten thousand…" Chika repeated the number, her mood sinking slightly.
Hara Kei could roughly guess her thoughts. Her situation could be explained by the Bombay blood type, but that didn't automatically make it the truth.
Her biannual hospital visits could be due to general frailty. Dislike of chores might be natural laziness. "Safety first" could be common sense. Her claim of fur allergies might just be a distaste for pets.
Compared with the improbable "Bombay blood type," these mundane explanations were more plausible.
This wasn't a game of whack-a-mole—you only get one chance.
This was an assassination attempt on the King of Qin.
Chika, playing the role of Jing Ke, only had one chance to strike.
If she asked and discovered her mother didn't have the Bombay blood type, how would she cope?
Of course, Chika had another choice: not to ask, and accept Hara Kei's explanation as truth.
After all, the explanation fit reality perfectly—and matched her hopes.
Better not to dig further. No need to ask. She already "knew the answer," didn't she?
Whether Chika would choose to investigate or accept the explanation, Hara Kei didn't know. In this matter, he was a complete outsider—a tree trunk for confessions. His prior answers had already slightly overstepped.
But—
"Fujiwara, have you ever heard of the 'Curse of the Upright Walkers'?"
Hara Kei still hoped that Fujiwara Chika was the same girl he knew in his past life. At least… he didn't want that radiant smile to be tainted by shadows.
..
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