Mutsumi is sweet and kind, but also responds poorly to stress. Sickly since childhood, she is constantly fainting or tripping or otherwise incapacitating herself whenever the need arises for intense physical activity. But her mind is keen, her eye farseeing, and her hands both gentle and nimble. She's noted both as painter, singer, and musician, absorbing most of the talents of her two parents, though she plays the mandolin instead of piano or saxaphone. She's also learned the arts of Trump from her father, and happily turns out trumps for anyone who asks. She also paints pictures as gifts for people, always remembering birthdays and holidays.
Mutsumi has the odd quirk of being simultaneously brilliant and a flake. She failed the entrance exam for Ohtori because she went to the wrong shadow and never showed up for it. But at the same time, she can argue philosophy with Travis, Yumi, and Haruna with great facility and talk rings around Princess Nanami, who is known to avoid her after having been shown up during a formal court dinner by Mutsumi.
Mutsumi has a flying turtle for a pet, named Tama-chan. Rumor has it that Tama-chan is now the Air Avatar of the Arcadian Pattern.
Mutsumi's heroic deeds during the Herald Crisis are too numerous to mention, but can be found in the UnS Timeline.
Mutsumi's accomplishments during the Herald Crisis surprised many, as she proved herself a Trump Master, and ventured bravely into danger time and time again. She finally broke off her long time pursuit of Keitaro, and hooked up with Princess Jacqueline and Prince Thoric. Now married, they rule Arcadia together with a gentle hand. And lots of watermelon. Rumors claim the Triumvirate and Motoko's Quartet have a yearly sex orgy. Most people discount this, and saying that around her father is a good way to get sent to Detention. When asked directly about the issue, Mutsumi laughed and offered some watermelon to the questioner.
Mutsumi is generally considered the premeire trump master of the family these days, as even Fuyutsuki has said she's better at it than he is. She's also one of the very strongest minds, and definitely the strongest of her generation.
Mutsumi is known to love both of her children dearly, though she gets along better with Minako than Makoto. She seems baffled by Ota Minor, and is known to be very fond of Random. She is also quite close to her sister, Princess Kaname.
Though she rarely sees him, she is known to be quite affectionate towards Nanbara, who makes her laugh. (She once called his father 'A big huggable mummy'). She seems to get along reasonably well with Kanako, though they have few dealings. She seems vastly amused by Miroku, and encourages him to keep trying with Uotani. She is on poor terms with Asuka, who she once lectured on manners for 3 hours straight. She is known to think Setsuna is a sweetie, and to be favorably inclined towards Akari. She also likes Aburatsubo quite a bit. Haru, for some reason, seems to irritate her.
Mutsumi seems a bit twitchy lately, perhaps due to the imminent Fair Folk invasion, her Aunt being revealed to have been out to destroy her kingdom and kill her family, and her husband having been turned into a woman and impregnated by Nemesis.
Despite this, she and her spouses helped repel an assault on Castle Amber recently.