If you find yourself with 43 of 44 total Steam achievements with Sonicomi, it's possible you are missing one or two articles of clothing required to unlock the True Sonicomi Master achievement.
Here is the complete list of items you should have (minor spoilers):
Cardigan
Slim jacket
Biker jacket
Sweatshirt
Jacket
Army jacket
Army jumper
Duffle coat
Cat ear poncho
Cat ear parka
Cat ear parka (hood down)
Concert jacket
Formal vest
Puffy vest
Formal jacket
Blouson
Enamel jumper
Stand-collar jacket (double)
Stand-collar jacket (single)
Open-chest apron
Apron
Bolero
Dragon jumper
T-shirt
Long-sleeved T-shirt
Y-shirt
Tank top
Tube top
Camisole
Frilly camisole
Tennis wear
Cheerleader uniform
Sailor uniform (summer)
Sailor uniform (winter)
Sweater uniform
Blazer uniform
Bikini Type A
Bikini Type B
Bikini Type C
Bikini Type D
Bikini Type E
American uniform
Naked Y-shirt
Gym clothes
Mini polo shirt
V-neck T-shirt
V-neck sweater
Turtleneck
Short-sleeved Y-shirt
Polo shirt
Open-backed blouse
Frilly blouse
Loose tank top
Soft pajamas
American cheerleader
Campaign girl
"Romeo & Cinderella"
See-through T-shirt
Training wear
Mouse bikini
Dragon T-shirt
Hot pants
Short shorts
Shorts
Pants
Sweatpants
Tight skirt
Pleated skirt
Soft pleated skirt
Tiered skirt
Gothic skirt
Tennis skirt
Cheerleader skirt
Sailor skirt
Blazer skirt
Bikini Type A
Bikini Type B
Bikini Type C
Bikini Type D
Bikini Type E
Bloomers
Heart-pounding hot pants
Formal slacks
Cocoon skirt
American cheerleader
Campaign girl
"Romeo & Cinderella"
Training wear
Mouse bikini
Dragon skirt
Anklet socks
Socks
Knee-high socks
Over-knee socks
Thigh-highs
Stockings
Loose socks
Fishnet tights
Garter belt
Dragon socks
Boots
Knee-high boots
Western boots
Thigh-high boots
Sneakers
Loafers
Pumps
Heeled sandals
Beach sandals
Indoor shoes
Slippers
Car slippers
Rocking Horse Ballerina
Pompom boots
Leather shoes
Work boots
High heels
Fashionable sandals
Pirate Bear slippers
Dragon sneakers
Rock star
Dream clothes
Bunny ear cardigan
Roasty, Porky, Noodles!
Babydoll
Frilly dress
Santa
Nurse
Goth loli
Blassreiter
Totori
Special voice actress
Sexy bikini
Naked apron
School swimsuit
Maid
Bondage
Bondage (cast-off)
Comfortable tracksuit
Racing swimsuit
One-piece dress
Waitress uniform
Group Sounds
Campus Life
Bunny girl
Lacy dress
Heart-pounding pajamas
Stray cat
White nurse
Kindergartner
Mustachioed tiger
Bunny maid
Kimono
Meruru
Fluffy snake muffler
Galaxy One
Ouka
Sweet Fairytale
More More Parka
Heartbreak turtleneck
Maid in Heaven
Race Queen
