Lambo is seven years old and still considered a total idiot by all that know him. Granted, he's in the top tenth percentile in his class, but this is always brushed off as being a result of having both Reborn and Gokudera constantly nagging him about work and I-pin's occasional (non-violent!) assistance. No one seems to notice that once they get past actually making Lambo start, that homework seems to take no time at all. Lambo is also seven years old when he first begins to seriously attempt at getting stronger. This is because, contrary to popular belief, Lambo is not stupid. He is a child that has spent his entire life attempting to impress adults that have a skewed perception of what constitutes appropriate behavior for a child his age. No one seems to notice that little boys are generally more volatile than little girls or that I-pin is naturally very mature for her age. No one seems to notice that the mafia standard for maturity and intelligence in a child is really no standard at all because no matter how young a person is, they are expected to act as an adult. This may be due to the misconception that the Arcobaleno are actual children or it may be due to the fact that what few children that have real positions in the mafia are generally over the age of ten and have spent inhumane portions of their lives being trained. But Lambo does not fit the mafia standard of smart. Even when he finally does hit the point at which he has met the mafia standard for intelligence, no one notices, because they have spent too long seeing him as a dimwitted weakling to see anything else. To asses him without prejudice.
It is at the age of seven that Lambo begins to seriously question the practicality of his use of the ten-year-bazooka. Lambo realizes that, all this time, he has been expecting himself to be much more capable ten years into the future. It is a logical assumption, after all. Ten years is a long time to get better. But, two years after he has started to use the bazooka, Lambo has improved very little in terms of fighting capability. It is two years, four months, and six days after the very first time that Lambo uses his bazooka that he is struck with the terrifying notion that he will still be using it ten years from now, never actually progressing in ability and always depending on his future self. A future self that will depend on another future self. Lambo fears that he will eternally be a failure. Someone who cannot fight his own battles. So, at the age of seven, Lambo Bovino, Tenth Guardian of the Lightning puts away his ten-year-bazooka. Lambo even takes the precaution of disabling it, having learned long ago how to fix his own bazooka since Gianni cannot be trusted with it. It will be a long time before anyone realizes that Lambo had a complex understanding of time-travel technology by the time he was six.
Lambo also begins to hit the age where he is less focused on his own needs and more focused on pleasing those around him. The only person he succeeds in ever pleasing is Mama. Coincidentally, Mama is the only one who has reasonable expectations of him. She is the only one that sees him as a developing child and not a nuisance.
Nearly three years after Lambo stops using his bazooka, I-pin returns to China to continue her training with the Arcobaleno Fong. So, at age ten, Lambo loses the only person that he has ever been able to come close to calling a friend. Like they have failed to notice so many things about Lambo, the familigia fails to notice that Lambo is severely maladjusted in school. Lambo does not understand why other children do not know how to fight or use weaponry. He does not know the games that they play or the shows that they watch. Lambo did not grow up around any children his age (bar I-pin, who had her own group of friends anyways) so he does not truly understand how to socialize with his peers. Lambo does, however, have an intimate knowledge on how to manipulate his words and actions so that others will do his bidding, so that he will always get what he wants. Apparently another thing that those around him have failed to notice is Lambo sitting right outside the door of many negotiation meetings.
It is when I-pin leaves that Lambo's personality begins to undergo its most drastic changes. Lambo gradually grows quieter and quieter. Lambo does not ask others to play with him as often and he does not see the need to cry anymore. After all, the only real comforting he has gotten when crying has come from either Mama, I-pin, or the ten-year-bazooka. Two of those are no longer options and Lambo is old enough now to feel guilty for making the already busy Mama worry about him. So Lambo truly learns to "tolerate."
Lambo doesn't actually train in front of others. He is too embarrassed over his weakness and lack of knowledge. So when Lambo put away his bazooka, he began to use the excuse of "playing with friends" to go train in a secluded part of the park (it was originally intended as a place for people to take long walks, but the residents of Namimori never really paid it much attention). Mama thinks that Lambo has finally made school friends and the others just don't care. They are glad to not have to deal with Lambo's antics. Consequently, it is a full year before anyone even notices that Lambo is not using his bazooka. Lambo has spend so much time away from the others at this point that they have all just assumed that he was using it when they were not around.
When Lambo is eleven years old most of the guardians are relocated to Italy. The only ones besides Lambo that have stayed behind are Mama and Hibari. Hibari's refusal to leave his hometown is tolerated only because someone needs to be able to handle affairs in Japan. Thus, the cloud branch of the Vongola stays where it is. Mama is left behind because no one wants to trouble her—to this day they all think that she is still blissfully ignorant. Lambo knows better. A lifetime of being pushed to the side has taught him to watch others (after all, what else can you do but watch when you are not allowed to join?). Lambo knows that Mama is underestimated, just like him. Lambo knows that Mama knows. He can see it in her eyes. He can see it in the way that she can brush off so much abnormality. They way that she smiles and knows just when to not walk into a room. The way that she is always ready to care for everyone. Mama is well aware of what is going around her but knows better than to change her ways. Mama understands that often times, her seeming innocence is what gives the others reason to keep going and that if she were to stop being what they want her to be, they just might start to fall apart. Mama is a pillar of support in the lives of the Vongola and both Lambo and Mama know it. But Lambo will never confront Mama about this. Mama fears being found out—that the delicate support of normalcy that she has created will fall apart and Lambo knows this, too. Lambo knows far more than anyone realizes.
It is when the rest of the guardians leave that Lambo begins to seriously learn how to use firearms. There is a shooting range and an armory in Namimori's secret base that Lambo long ago figured out how to gain access to. Reborn has gone away with the rest and the only ones left in Namimori that Lambo is hiding his training from are Hibari and his men. But they do not care about him. They are too busy elsewhere. He is nothing but a vague civilian (herbivorous) blip on their radars. Lambo suspects that Kusakabe (of all the people he has ever met, Kusakabe!) has an inkling about Lambo's existence. But he never confronts Lambo in the same way that Lambo never confronts Mama. They all know that to open up their secrets would cause more damage than good. Lambo briefly wonders what it is that Kusakabe is hiding, but quickly puts the matter out of his mind. It is none of Lambo's business. After all, Kusakabe is enough like himself that he trusts that the man is doing what is best.
What Lambo has not told anyone is that his hands are stained with the blood of others. Everyone would like to believe that Lambo is fully innocent when it comes to seriously hurting others (bar the-future-that-never-was incident). This is a complete lie. Lambo killed his first man at the age of three-and-nine-months in an act of self-defense. Strange men had gone after him in an attempt to hurt his caretakers and Lambo had unconsciously released to much electricity from his tiny body that he had killed not just the five men surrounding him but the all the power within a kilometer radius as well. As it turns out, his caretakers hadn't noticed that Lambo had been missing for the three days prior, nor did they particularly care that he had come home sick, dirty, and bruised. Between that time and when he was finally sent to Namimori, Lambo had killed at least another six dozen men. Lambo was not lying when he said that he was an assassin. This happens to add to Lambo's social maladjustment, as no one has ever considered that Lambo does not understand the value of human life. Aged eleven, Lambo still fails to understand why some of his fellow guardians have problems with killing their enemies.
When Lambo is twelve years old, there is a large gathering at Namimori in which the entirety of "the old gang" is gathered. At this time Lambo has mastered the use of most firearms and multiple forms of martial arts. Lambo still has no friends despite being at the top of all his classes. Once again, no one notices, or even bothers to ask. The most Lambo gets is the off-hand questioning of "How's school going?" By now Lambo knows that anyone who asks this question doesn't actually care how school is going and is simply going through the motions of polite conversation. Lambo doesn't even try to make conversation and simply answers with an "It's going alright." Lambo spends most of the week-long gathering trying to avoid the others. He goes back to that old park and, for lack of better options as the shooting range is now out of question, to the library. By the time everyone leaves Lambo has begun to develop as great interest in biology. He pays particular attention to the concept of bioelectricity. Lambo spends much of the next year trying to gain a better control to the electricity that he is so naturally attuned to. When he has finally gained enough control, Lambo spends another six months learning how to use this control in order to incapacitate another person via open nerve endings and pressure points. Lambo is now nearing his fourteenth birthday. Mama still thinks that Lambo has many friends. The other guardians still think that he is stupid, albeit a bit calmer than before.
It is when Lambo is fourteen-and-five-months old that he is finally sent for to go to Italy. This decision, ironically, was not made because the Vongola wanted him there. It was made because the Bovino family wanted him closer at hand. They are aware of Lambo's previous kills and his massive potential. They want to make use of it. Tsuna and the others are okay with having the Bovino's deal with Lambo's "introduction" into mafia works—after all, it spares them the trouble of handling it themselves. They still don't know that Lambo has long ago been well aware of the finer points of just about everything there is to know. It is exactly six months later that Lambo moves from working with the Bovino's to properly working for the Vongola. The Bovino familigia does not bother sending a summary of Lambo's previous work to the Vongola and no one in the Vongola seems to notice or care. This results in Lambo spending most of his time with the Vongola in the mansion doing simple tasks, such as entertaining important guests, or going over finances.
It is when the newly-fifteen Lambo starts getting switched out with his five-year-old self that anyone realizes just how much Lambo has changed. Where Lambo is normally a shadow that moves in silence, his younger self is loud, vibrant, and demanding of attention. Most chalk it up to age having matured Lambo. Reborn, Yamamoto, and Tsuna are the ones to really take issue with this contrast in behavior. Yamamoto observes Lambo when he thinks the other isn't aware (but he is, he's always been). Reborn keeps giving him these looks, like he can't trust Lambo, as if he expects Lambo to become just as volatile as Mukuro. However, Lambo knows very well that Reborn will do nothing until he has dug up every secret that Lambo has to offer. It is Reborn's way, to act only when he has knowledge of everything. Another of the many things that Lambo knows. Tsuna simply doesn't know how to handle the issue that is Lambo and pushes it to the side due to being too busy and having "more important things" to deal with. Little does he realize that he's just doing what everyone else has been doing for the last ten years. Unexpectedly, the only one that seems completely unsurprised with Lambo's personality change over the years is Chrome. But, when Lambo sits down to think about it he realizes that she is the closest that anyone will ever get to being in his situation. Chrome has spent much of her life being written off as both useless and worthless and, when she had stopped being either, no one had really noticed. As great of an illusionist Chrome was, everyone else always saw Mukuro's work instead. She knew exactly what it was like to be ignored and invisible even though she was right there in front of everyone else.
Along with intelligence, Lambo is blessed with an excellent memory. A memory that allows him to remember the exact time and date at which he, or anyone else, will be switched out by the ten-year-bazooka. Lambo takes to manipulating the situations around himself so that no mission or lives are compromised due to unfortunate timing. At worst, he once had to swipe one of Shamal's mosquitoes and make himself sick so that his younger self would not end up in the middle of a VERY important peace negotiation. The chaos caused by "Little Lambo," as his younger self had been dubbed, would have been severely disastrous to the creation of a very tentative ceasefire agreement.
It is when Lambo supposedly kills his first man that all hell breaks loose. Figuratively speaking, of course. Lambo is sixteen and finally considered old enough to go on real missions. Ironically, Lambo's "first" kill had nothing to do with a mission. The guardians were on their way back from a social function when their limo had been ambushed. In the resulting melee nothing much was actually noticed about Lambo's fighting style or skill. Everyone was too busy dealing with their own enemies. The most anyone saw was a flash of electricity, or a blur of cow-print in their peripheral vision. What everyone DID see, however, was Lambo gunning down a man at point-blank range. They also saw Lambo shoot the man a second time, just in case, with a completely nonchalant look on his face. It seemed so out of character that, for the rest of the silent car-ride home, no one even remembered to ask where Lambo had gotten the gun in the first place.
Later that night, during dinner, Tsuna had asked Lambo if he was alright and if he wanted to talk about the events earlier that day. Lambo had given him a mildly confused look and simply said "Why? It's not like anything spectacular happened." It was Yamamoto who spoke next, his skill as a hitman allowing him to ask what could be considered the right question. Yamamoto asks Lambo how old he was when he killed his first man. The others at the table want to object but know better than to say anything when they see the stone-cold expressions in both Yamamoto and Reborn's eyes. Instead, they wait with baited breath as Lambo opens his mouth to speak. "Three-and-a-half." is the simple response. In the silence that follows Lambo suddenly feels the need to elaborate. He hasn't felt this nervous and exposed in years. "It was a freak accident. Self-defense." Lambo is no longer maintaining eye-contact and his voice is much quieter. Reborn asks the next question, because while his digging into Lambo's past has not allowed him to access the details of Lambo's mission archives (as influential as he is, Reborn still cannot breach the privacy and security of an allied familigia without political repercussion) but the fact that there is an archive for Lambo at all leaves Reborn with a great deal of suspicion. "How many people have you killed since then?" Lambo is silent for a moment because, although he has an excellent memory, he has never actually bothered to remember most of his kills. Lambo still hasn't learned that human life holds value and so, to him, each individual kill is not particularly notable. As much as the fact that Lambo has to actually think to get his answer bothers those around him, it is his final answer that is most disturbing of all. "436. No, wait, 37. I think. I don't know. Something like that. I don't remember most of the ones from before I met you guys…" Lambo is scratching his cheek and looking up at the ceiling tiles (they replaced the cracked lavender tile, he thinks idly).
The next day Tsuna has the Bovino familigia's file on Lambo on his desk, complete with reports on every mission he has ever gone on, a full catalogue of Lambo's abilities, and a full set of academic records. Tsuna also has notes form all of Lambo's teachers on his behavior during his school years, security records from the hidden base, testimonies from random citizens of Namimori about the odd little boy, and notes on every incident in which someone has been switched out by the ten-year-bazooka. There are even records on the severely diminished ammunition stock in the Japan base, despite it having supposedly not been touched in years (Hibari and his men, in true cloud spirit, supply their own ammunition).
It doesn't take long to put the pieces together. Lambo, at age sixteen-and-ten-months, is finally seen by the guardians of the Vongola. Lambo has become a monster under their very eyes and without being noticed. None had realized the full extent of Lambo's social maladjustment, his warped outlook on the world, his fighting ability, his intelligence, his….everything.
Later that week there is a gathering of the Vongola's inner circle to discuss the state of affairs concerning Lambo. There are suggestions to use him on the front lines, as a strategist, to send him on vacation to learn how to function like a normal person, even a bid to send him to work for the Varia (which, frighteningly enough, the members of the Varia seriously consider). Eventually, someone asks the question that is weighing on all their minds. "Why didn't we realize this sooner?"
It is Chrome that breaks the long silence that follows. Though she speaks quietly, she is heard by all. "It's because no one bothered to look." She walks out after her statement, leaving a silent room full of unpleasant emotions. But they know she's right and they marvel at how badly they've messed up,