Your companion 相棒
Who walks beside you, what they wear, and why none of it changes how hard a card is.
You pick a 相棒 companion before your first review and it walks the whole journey with you. There are 12 to choose from (a capybara, a shiba, a fox, a tanuki, an owl, a deer and others), and they are all equal. None is stronger, faster, or better at anything.
Why they are equal
Because the alternative is a trap. The moment one species answers cards better, choosing your companion stops being a choice about who you want beside you and becomes a puzzle with a correct answer - and a beginner making that choice on day one, before they know anything, gets it wrong and carries it for a year.
So the difference is entirely in the drawing. Choose the one you want to look at.
They wear what you have earned
A companion is dressed in your rank. All 6 ranks have their own outfit, drawn at the same thresholds as the titles (Deshi, Samurai, Bushi, Ronin, Daimyo, Sennin), so a promotion is something you see rather than something you are told.
On top of that, anything you have earned or bought with 文 mon can be worn: hats, haori, a fan, a lantern, something in each hand. Pieces picked up at stations on your road are bound to the place they came from, so a loadout ends up being a record of where you have been.
All of it is cosmetic. Not one item changes a card, a schedule, a level or a purse.
Pets
Pets お供 attendants hatch from things you do - reaching somewhere, finishing a season, ascending an item, bringing a friend. They are collected rather than bought, and several of them cannot be bought at all, which is what makes seeing one on somebody's profile mean something.
They also grow in stages, so a pet is a small record of how long you have had it.
complete one season's 祭事 lane
reach 500 mastery points
hold a 7-day streak
one perfect batch of 10+ reviews
master 50 facets (マスター)
arrive at Edo (江戸入り)
invite a friend - you both hatch it
master 50 kana
master 100 vocabulary facets
master 300 kanji facets
reach 3,500 mastery points (侍)
hold a 60-day streak
ten perfect batches
hold 500 mon at once
reach level 20 (武士)
own 10 gear items
ascend an item to 妖 (tier 4)
walk four roads
reach level 50 (仙人)
Every one of them, and every item and road, has a page in the 図鑑 illustrated record - and nothing in it is ever a dead end: an entry you have not earned yet tells you how to earn it.
One companion, for the journey
Your species is a lifelong choice. The one exception is the 開祖 Founder seal, a one-time purchase that carries a single switch - spent once and gone, never expiring, and surviving every downgrade. It exists because a choice made on day one, in the first minute, is the one a person is most likely to regret.