She's a Homunculus that's being attacked by a White Tiger.
MC tank it while the other kids damage it, ezwin.
The girl lose consciousness at the end of the fight, MC checked her state and realized from the magic stone embed in her chest that she's a homunculus.
So hiding that fact for now, he decide to ask for the merchant to drop him on near his hometown first and he'll take care of this girl for now. (obviously, both the merchant and the kids are impressed by his tank power)
When she woke up, he noticed that she showed a surprised expression, unlike the typical expressionless homunculus he knew.
Then she leapt off him, saying she won't be disposed of then start casting magic.
At this point he knew she's definitely not a normal homunculus, since the ones he knew are basically living dolls that only follow orders and also have no combat skills.
After eventually convincing her he's not an enemy and told her she's free to do whatever she want.
Girl "But...I don't know what to do"
She's only lived by obeying orders until now, and somehow survived + escaped from the disposal site only to run into that tiger which led into her running into him.
He suggest for her to try becoming adventurer, given that she can fight and homunculus looks exactly like human, so long as she hide the magic stone on her chest nobody would know she's one.
Girl "But, I can only appraise people's skills"
MC O[] O
He immediately ask her to identify his skills
Girl "Sure"
MC "So easily?"
Girl "It's my job"
And so he gets to learn what his last 2 skills, both of SSR rank (SSR -> SR -> R -> N from highest to lowest) do, since they're skills nobody ever gotten before.
Scan result (requires handholding, #LEWD)
Girl "You have 4 skills. [Taunt], gain the maximum attention of your enemies."
"Next, [Healthy Body], immune to abnormal statuses, and body become as sturdy as it can be"
"Next is Life Conversion, able to convert damage taken into strength"
MC - Oh, I DO have an attack skill huh.
"Finally, Sacrificial Shield, this skill makes you take damage in place of people you think of as allies. While covering allies, if that person is buffed, your own sturdiness also increases"
He then thanked her, for solving the questions he's had before.
She was surprised again, because nobody ever thanked her before.
Back to the question of how she plan to live from now on, he decide he'll help her out until she figure out what to do, as thanks for identifying his skills.
Girl "....Understood. Thank you very much"
MC "I'm Rude. Let's get along"
Girl "I'm called Homunculus. Master (kana 'master', not 'goshujin-sama' master) , I'll be in your care from now....I, do not have a name"
Thinking that she'll need a name if she will live in society, MC start pondering, then he noticed some flower petal on her cloth.
It's from Lunafia flower, his imouto's favorite flower.
MC "How about Luna?"
Girl "Luna?"
MC "Yeah"
Girl "Luna....Luna....Yeah. From now on I'll live as Luna"
She smiled.
MC was still not used to homunculus showing expressions, but this isn't so bad.
Luna "What's wrong, Master?"
MC "Can't you stop with the Master thing?"
Luna "No, this is the only thing I won't budge on. You saved my life, that's why let me treat you with respect."
MC - ....She's got some stubborn part too. Not at all like a homunculus,but that's not a bad thing.
And so the two makes their way to his hometown.
tl;dr the waifu this time is a homunculus whose first conversation with MC start with a fire bird and a knife stab.