Learn Hardcore French: C'est toi que je veux rencontrer aujourd'hui.

After c'est, French uses the stressed (tonic) pronouns: moi, toi, lui, elle, nous, vous, eux, elles.
tu is a subject pronoun used before a conjugated verb (e.g., Tu viens), not after c'est. So you say C'est toi, not C'est tu.

What does the C'est … que … structure do?

It’s a cleft sentence that adds emphasis or focus to the element after c’est.
C’est toi que je veux rencontrer highlights toi (you in particular).

Why que and not qui here, and what exactly is que doing?

Use que when the focused element is the direct object inside the relative clause: … que je veux rencontrer (object of rencontrer).
Use qui when that element is the subject of the clause: C’est toi qui viens.
Here, que is a relative pronoun referring back to toi and serving as the direct object of rencontrer.

Can I drop que and say C'est toi je veux rencontrer?

No. In a cleft sentence, the relative pronoun (que/qui) is required to link the focus to the clause.
Without que, the sentence is ungrammatical.

What’s the neutral, non‑emphatic way to say the same thing, and where does the object pronoun go?

Neutral version: Je veux te rencontrer aujourd’hui.
With verb + infinitive, the object pronoun goes before the infinitive it belongs to:
- Correct: Je veux te rencontrer.
- Incorrect: Je te veux rencontrer.

Can I say both toi and te in the same sentence, like C’est toi que je veux te rencontrer?

Not in the cleft structure: C’est toi que je veux te rencontrer is incorrect (it doubles the object).
However, in left-dislocation you can say: Toi, je veux te rencontrer (colloquial, with a comma intonation).

Why rencontrer and not retrouver or voir?

rencontrer: to meet (often first time or in a meeting context), transitive with no preposition.
retrouver: to meet up with (someone you already know, planned).
voir: to see (commonly used for meeting up too).
Examples: Je veux te rencontrer, Je veux te retrouver, Je veux te voir — each has a slightly different nuance.

Do I need a preposition with rencontrer?

No. Rencontrer is directly transitive: rencontrer quelqu’un.
Avoid rencontrer avec quelqu’un.

Can I move aujourd’hui, and does it change the meaning?

Yes. It usually goes at the end, but you can move it for style/emphasis:

C’est toi que je veux rencontrer aujourd’hui.
Aujourd’hui, c’est toi que je veux rencontrer.
If you want to emphasise the time rather than the person, use a time-cleft: C’est aujourd’hui que je veux te rencontrer.

How do I say it to one person formally, or to several people?

Formal/plural you: C’est vous que je veux rencontrer aujourd’hui.
Neutral version: Je veux vous rencontrer aujourd’hui.
For a plural group you can also see: Ce sont eux/elles que je veux rencontrer (in speech, C’est eux/elles que… is common).

How do I negate this sentence?

Cleft: Ce n’est pas toi que je veux rencontrer aujourd’hui.
Neutral: Je ne veux pas te rencontrer aujourd’hui.
(In casual speech, the ne is often dropped: Je veux pas te rencontrer.)

How can I make it sound more polite/softer than veux?

Use the conditional or softer verbs:

C’est toi que je voudrais rencontrer aujourd’hui.
J’aimerais te rencontrer aujourd’hui.

How would this look in the past? Any agreement to watch for?

With a past meeting: C’est toi que j’ai rencontré(e) aujourd’hui.
The past participle rencontré agrees with a preceding direct object: add e if the person is female, s if plural (e.g., C’est vous que j’ai rencontrés for several people).
For a past desire: C’était toi que je voulais rencontrer.

Why is it que je and not qu’je?

Elision (qu’) happens before a vowel sound or mute h. Je starts with a consonant sound, so no elision: que je.
Compare: C’est toi qu’il veut rencontrer (elision before il).