niたいtaiするsuru
1.

In relation to or in connection with a particular subject or entity.

2.

Expressing a viewpoint or attitude towards someone or something.

3.

Indicating a direction or target for an action or sentiment.

4.

Concerning the implications or considerations associated with a specific matter.

Example:

これが私の手紙に対する彼の返事だ。

たいtaiするsuru
1.

To stand or be positioned directly opposite another, suggesting a physical or metaphorical confrontation.

2.

To engage with someone or something in a particular manner, indicating a specific attitude or response toward the counterpart.

3.

To target or direct thoughts, actions, or concerns towards a specific issue or object of interest.

4.

To draw comparisons or contrasts between two entities, recognizing distinct differences or relationships in their attributes.

5.

To confront an opponent or rival, often in a competitive context, as in a challenge or contest.