WARNING: The following contains spoilers for Boruto: Naruto Next Generations Episode 229, "Breach of Orders," now streaming on Crunchyroll.
In both the Boruto anime and manga, Shikamaru has not been as accepting of Kawaki as the rest of the gang. On the contrary, he's been quite derisive and insults the teen at any given point, even after Kawaki helped them take down Isshiki. But while fans thought it may have been due to Shikamaru fearing the boy's power, the recent TV fillers hinted he may hate Kawaki for one shocking, relatable reason: he is a stark reflection of a negligent past.
It's revealed when Kawaki laughed off Naruto's suggestions that he take D-rank missions to start his journey as a Hidden Leaf shinobi. Kawaki doesn't believe in community and protecting the village that way, throwing insults back at the council.
The Hokage remained adamant that being a genin would help him become the guardian he wants to be but Kawaki, stubborn as ever, reiterated his talents can allow him to become a protector on his own terms. When he departed, Shikamaru, as expected, lashed out at his insolence and lack of gratitude, wondering how Naruto puts up with such sulking and broody nonsense at home with the adopted son.
But it's the last words Kawaki left him with that really triggered the adviser, calling the shinobi training a "real drag." These were the same words Shikamaru used to describe his own training, which turned him into the laziest character in the Naruto era. He was the most brilliant tactician but this was his massive flaw, highlighted when Shikamaru forfeited the Chūnin Exam fight against Temari.
Shikamaru felt he didn't have enough chakra to beat Temari after he locked her in his Shadow Possession technique, but it was him not wanting to keep advancing. Even his own teammate, Chōji, kept telling people Shikamaru was lazy and loved giving up, which is something he regretted as he got older. His father Shikaku worked in the ninja sensory team, after all, so they often fought over this lackadaisical attitude as he felt his son wasn't living up to his potential. More so, the father thought it was disrespectful and selfish to dishonor the village by avoiding fights, sleeping during school and leaving other ninja to do the heavy lifting.
Shikamaru changed his ways but sadly lost his dad in the Kaguya War, which is why he always wished he could go back and be more assertive to impress his idols. Luckily he's seen his son, Shikadai, be the total opposite in Boruto -- hardworking and proactive -- but when Kawaki threw this jab at him, Shikamaru was quickly reminded of his own past failures.
Sure, he might not like Kawaki being a WMD and wildcard, but he does want the prodigy to tap into and hone his craft. Shikamaru knows the boy could be great like Naruto and Sasuke -- especially now that Konoha is more vulnerable than ever.