The following content contains spoilers from KonoSuba: An Explosion on This Wonderful World! Season 1, episode 2, accompanied by details from the manga and Light Novel. The son of the Crimson Demons' esteemed shoemaker (and next in line to inherit the business) made his first appearance with a minor role in KonoSuba The Movie: Legend of the Crimson Demons and has been seemingly forgotten since.
Fortunately, his quirky characteristics are due to be fleshed out more extensively during Megumin's spin-off series, An Explosion on This Wonderful World! Megumin seems to be quite familiar with Bukkororii's (also spelled Bukkorori) antics; so much so that her classmates assume that the pair are related. However, they are little more than neighbors who, as fate would have it, become accomplices of sorts. But only when convenient.
Big Brother Bukkororii
Like many of the other Crimson Demon Village residents, Bukkororii is unashamedly a NEET; however, he is rather productive with his abundance of free time, as he is constantly cultivating his obsession with Soketto. Don't be fooled by his intense stalker tendencies because Bukkororii refuses to associate with such an abhorrent term; he is not a stalker, he is just madly in love! She is the most beautiful Crimson Demon in the village, after all.
The fact that Bukkororii technically has nothing going for him is not indicative of his skill level; there is much truth to his whole "Advanced Magic wielder" flex. However, he does not always use these talents for their intended purpose. His Light Of Reflection spell, for example, can render Bukkororii invisible, which is undeniably advantageous on the battlefield but is perfect for snooping around Soketto, too! However, regardless of his efforts, the lovestruck chuunibyou simply can't work up the courage to approach Soketto and strike up a conversation like a normal person, which is where Megumin comes in.
As long as she can get something out of it (like a free meal or a bodyguard during trips through the forest) Megumin acts as her "big brother's" wingman and offers up relationship advice, all the while pointing out the glaringly obvious pitfalls in his current rizz-free strategy. However, she claims no loyalty to Bokkororii's cause and will ditch him for bigger and better things at the drop of a hat, particularly when his stalker side inflates too fiercely, becoming impossible to ignore.
Bukkororii's Better Half
Soketto is more than just a pretty face and can hold her own during combat, although her ability to respond to social cues could do with some work, as she isn't so great at reading a room. For example, she has noticed Bokkororii hanging around quite frequently and becomes angered by his presence, however, not because she is creeped out. In Soketto's mind, this strange behavior can only mean one thing: he must hate her for some random reason. She's that type of anime girl who needs situations like these spelled out to her; such "subtle" hints are useless to the pretty powerhouse.
Soketto's Light Novel introduction is much more epic than in KonoSuba The Movie, where her (barely even) one-liner "Now...It's born" has little to no dramatic effect. In strong contrast, Soketto's original LN opening statement is:
“Please rest in peace. I won’t forget you all. That’s right, your existence will be engraved forever… In the memories of my soul…!”
This sexy witch is as chuunibyou as the rest of the Crimson Demons and is done a disservice in the anime, which is such a shame considering her substantial fan-service appeal!
Whilst being a formidable mage with a flair for Lightning magic, Soketto makes a living by being the town's fortune teller, and no, it's not all just smoke and mirrors. As with any Divination technique, the future is not always crystal clear and there should always be room for potential error; however, taking heed of Soketto's words is recommended. Unfortunately for Bukkororii, his chosen paramour is seemingly not in the cards, now or in the future (no surprise here!) After "saving" her from a rogue monster, Soketto offers to read his fortune and search for signs of his destined lover, the results of which inexplicably come up blank. Perhaps the crystal ball's clarity was meant to reflect Soketto's face on the surface? Or maybe Bukkororii's obsession will get the better of him in the end.
Bukkororii's (Intermittent) Brilliance
Despite his many, many flaws, Bukkororii is actually one of the most talented wizards in the Crimson Demon Clan (who has basically become a NEET in order to accommodate his obsession.) If it weren't for his time-consuming stalker hobby, Bukkororii could easily be considered Megumin's greatest competition. His lack of life experience has not hindered his magic abilities in the slightest, allowing him to wield some of the highest-level advanced magic known to the Crimson Demon Clan.
Singlehandedly eliminating a monster is no problem for Bukkororii; if only he had the appropriate ambitions! This mind-boggling mage has a lot in common with Aqua (in the sense of wasted potential), although at least it takes a lot less coaxing to convince Bukkororii to fight. His Light of Saber and Inferno in particular are quite glorious, while his chuunibyou factor is also on point; making him one of the most talented NEETs in town. Megumin should be grateful for Bukkororii's manic infatuation, which essentially removes this competitor from the running for the best Arch Wizard in the business.