sono sensei ha kibisisou ni mieru keredo, zissai ha totemo ii hito desu.

その means that and points to a specific teacher that both speaker and listener can identify from context.

So その先生 = that teacher.

This is different from just 先生, which could mean a teacher or the teacher depending on context.

A quick comparison:

• この先生 = this teacher
• その先生 = that teacher
• あの先生 = that teacher over there / that teacher we both know

は marks その先生 as the topic of the sentence: as for that teacher...

The sentence is basically saying:

• As for that teacher, he/she seems strict, but is actually a very nice person.

Using は sets up the person being talked about, and the rest of the sentence gives information about them.

厳しい means strict.

厳しそう means looks strict or seems strict.

The ～そう form is often used to describe how something appears from the outside.

So:

• 厳しい先生 = a strict teacher
• 厳しそうな先生 = a teacher who looks strict

In this sentence, the speaker is not directly stating that the teacher is strict, only that they give that impression.

When ～そう is attached to an い-adjective to mean looks/seems, you usually remove the final い first.

So:

• 厳しい → 厳しそう
• おいしい → おいしそう
• 高い → 高そう

So 厳しいそう would be incorrect for this grammar pattern.

The に is used because 見える is being modified adverbially.

Think of it like this:

• 厳しそう = strict-looking / seeming strict
• 厳しそうに見える = appears in a strict-looking way

This is a common pattern:

• 元気そうに見える = looks energetic
• 悲しそうに見える = looks sad
• おいしそうに見える = looks delicious

So the に turns 厳しそう into a form that can describe how someone appears.

見える can mean to be visible, but in this sentence it means to look or to appear.

So 厳しそうに見える means:

• looks strict
• appears strict
• seems strict

This use is about the impression someone gives.

Compare:

• 山が見える = I can see the mountain / the mountain is visible
• 彼は元気に見える = he looks energetic

Both can work, but they are slightly different in nuance.

• 厳しそうです = seems strict
• 厳しそうに見える = looks strict / appears strict

見える emphasizes visual impression a bit more. It suggests the speaker is judging from appearance or outward behavior.

So this sentence gives the feeling: At first glance, that teacher looks strict...

けれど means but, though, or although.

It connects two contrasting ideas:

• その先生は厳しそうに見える
• 実際はとてもいい人です

So the contrast is:

• The teacher looks strict
• But in reality is a very nice person

けれど is a very common and natural way to express contrast. Other similar forms are:

• でも = but
• が = but
• けど = but (more casual than けれど)

実際 means reality, actually, or in fact.

With は, 実際は means something like:

• in reality
• actually
• as a matter of fact

It contrasts appearance with reality.

So:

• 厳しそうに見える = looks strict
• 実際は = but actually / in reality
• とてもいい人です = is a very nice person

Here は adds contrast or emphasis.

実際は highlights the idea of in reality, as opposed to how things seem.

So the sentence has two contrastive points:

• その先生は...
• 実際は...

This second は helps frame the second clause as the true situation.

Without going too deep, you can think of 実際は as a very common chunk meaning actually / in reality.

Both いい and よい／良い mean good.

In everyday speech, いい is much more common.

So:

• いい人 = nice person / good person
• よい人 = also correct, but sounds a bit more formal, careful, or written depending on context

Learners often notice that the dictionary form is historically related to よい, but in normal conversation いい is extremely common.

It often means nice person, kind person, or good person, depending on context.

In this sentence, とてもいい人です most naturally means:

• a very nice person
• a very kind person

It does not necessarily mean perfectly moral in a heavy philosophical sense. It usually describes someone as pleasant, considerate, warm, or decent.

とても means very.

So:

• いい人です = is a nice person
• とてもいい人です = is a very nice person

It simply strengthens the description.

Here 人 literally means person, but in Japanese いい人 is a very common expression.

It often means:

• a nice person
• a kind person
• a decent person

So while the word-by-word meaning is good person, the natural meaning is usually nice person.

Yes, very naturally.

The sentence suggests an appearance vs. reality contrast:

• At first, the teacher gives the impression of being strict.
• But in reality, the teacher is very nice.

So it can imply that the speaker’s first impression was incomplete or somewhat misleading.

It is polite neutral Japanese.

Clues:

• です at the end makes it polite.
• けれど is natural and moderately polite.
• The sentence is not stiff or highly formal, but it is more polite than casual speech.

A more casual version might be:

• その先生は厳しそうに見えるけど、実際はとてもいい人だ。

A slightly more formal or written version might use:

• その先生は厳しそうに見えますが、実際はとてもいい人です。

Yes, ～そう can sometimes feel like seems likely to be..., but in this sentence, because it is followed by 見える, the meaning strongly leans toward looks / appears based on outward impression.

So:

• 厳しそうです = seems strict
• 厳しそうに見える = looks strict

The second one is more clearly about appearance.

A helpful breakdown is:

• その先生は = as for that teacher
• 厳しそうに見える = looks strict
• けれど = but
• 実際は = actually / in reality
• とてもいい人です = is a very nice person

So the pattern is:

Topic + appearance/impression + contrast + reality + conclusion

This is a very common structure in Japanese when comparing first impressions with the truth.