Wataru has short, light-Salmon colored hair and brown eyes. He wears a long-sleeved yellow and pink jacket with star motifs, and white long-sleeved shirt underneath as well. He also wears lacy shorts and yellow-colored shoes. He carries around a stuffed rabbit in his jacket pocket, similar to the one his older brother Masaomi has. He also wears a lanyard with a cat pocket attached to the end to carry his phone.
In season 2, he appeared to be taller, as he gained 10 centimeters (150cm now). His hair is much thicker, and seen to have a little ponytail in the left side, with a teddy bear as its cover. Wataru now wears the Bright Centrair Uniform; a white coat that has a cross-shaped symbol at the below the collar, with a blue with gold-striped ribbon sticking on it. From the inside, he wears a vest that has 5 buttons, and a polo under it. His short shorts in season 1 changed too, as he wears a striped pants, with a pink, fluffy and tamagotchi-like toy near his pocket. The yellow-colored shoes before have changed into a pair of big brown boot-like shoes. However, Wataru still has the rabbit toy from season 1 in his coat's pocket.
Wataru is very a sweet and honest, albeit spoiled, young boy who cares deeply for his brothers and his new stepsister. He is very playful, and often gets away with acting spoiled due to his older brothers’ protectiveness over him.
He is also quietly confident and determined, willing to persevere in the battle for Ema's heart. He is also aware that his age serves as limit in the contest, but is willing to wait and make his move when he is older.
Wataru first appeared differently in the Anime and Novel. In the light novel, he accidentally bumps Ema and Juli, who is driving a bike, near the Sunrise Residence gate, later, he introduces himself with Masaomi and apologizes. In the Anime, Ema saw Masaomi and Wataru in the gate, saying hello to her.
In season 2, Wataru called Ema, whom he met near an arcade in the mall. They talked for a while, and saying she shouldn't call him Wataru-chan anymore, despite that now that he has grown up, he will be Ema's boyfriend really soon, and she should call him Wataru-kun like his brothers.
After their father died, Masaomi became a father figure to him. Masaomi made him his favourite rabbit toy and has a similar one in his pocket as well.
When he first met Ema, he already liked her and was happy when he knew that she was going to be his sister. He is also aggressive towards Ema, firmly stating that he will "become a man who is worthy of her."
Wataru seems to like Juli almost as much as he likes his rabbit toy (Not quite though), as seen in Episode 6 when he took him by the ribbon to look at pictures. He treats him like his rabbit doll.
- His name means 'to extend'/
- He is the thirteenth and youngest son of the Asahina Family.
- He loves all sorts of cake.
- He has many hobbies such as karate, soccer, collecting bugs and imitating his brothers.
- He doesn't want to be treated as a kid.
- Ukyou is likely the only brother who is very strict to Wataru.
- The episode where Natsume falls in the water, due to Wataru, was portrayed differently than in the novels.
- He likes Ema.
- He said he will never lose to his brothers.
- He says to Ema he will be a man who is worthy for her.
- He gets very excited when Ema makes something special for him.
- He gives his elder brothers nicknames such as "Fuutan" and "Nakkun".
- He wants to be a CEO when he grows up.
- For 2014 April Fool's, on the Brothers Conflict Sylph Dengeki web page, the female Wataru was named Wataho (弥帆).
- He shares the same Zodiac sign with his triplet brothers, Tsubaki, Azusa and Natsume, Capricorn, the Goat.
- Wataru has also the same voice actor with Kanato Sakamaki from Diabolik Lovers, Eren Jaeger from Shingeki no Kyojin/Attack on Titan, and Finnian a.k.a. Finny from Black Butler.
- He has an ahoge.