キャラに追従するカメラ

キャラを用意

Colliderの形状がカプセルなどの場合は、転がってしまわないように、RigidbodyのFreeze Rotationのx,zにチェックを入れる。

カメラをキャラの子要素にする

Chara
　└ MainCamera

スクリプトで操作する

カメラに以下のスクリプトをアタッチ

CameraController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CameraController : MonoBehaviour {
    public Transform target;
    public float smoothing = 5f;
    private Vector3 offset;

    void Start () {
        offset = transform.position - target.position;
    }

	void Update () {
        Vector3 targetCamPos = target.position + offset;
        transform.position = Vector3.Lerp(
            transform.position,
            targetCamPos,
			Time.deltaTime * smoothing
        );
    }
}

汎用スクリプトを使う

Scripts > UnityStandardAssets.Utility > Smooth Follow

もしくは

Scripts > UnityStandardAssets.Utility > Smooth Target

参考
Unityでカメラの設定とキャラクターの追従をさせる

常にプレイヤーの進行方向後ろから追従させる

背面ベクトルを何倍かさせてカメラの位置ベクトルを決定する。

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ChaseCamera : MonoBehaviour {

	private GameObject player;
	private Vector3 prevPlayerPos;
	private Vector3 posVector;
	public float scale = 3.0f;
	public float cameraSpeed = 1.0f;

	void Start () {
		player = GameObject.Find ("CameraTarget");
		prevPlayerPos = new Vector3 (0, 0, -1);
	}

	void Update () {
		Vector3 currentPlayerPos = player.transform.position;
		Vector3 backVector = (prevPlayerPos - currentPlayerPos).normalized;
		posVector = (backVector == Vector3.zero) ? posVector : backVector;
		Vector3 targetPos = currentPlayerPos + scale * posVector;
		targetPos.y = targetPos.y + 0.5f;
		this.transform.position = Vector3.Lerp (
			this.transform.position, 
			targetPos, 
			cameraSpeed * Time.deltaTime
		);
		this.transform.LookAt (player.transform.position);
		prevPlayerPos = player.transform.position;
	}
}

正面ベクトルをとれば前から撮影するカメラに変わる。

void Update () {
	Vector3 currentPlayerPos = player.transform.position;
	Vector3 frontVector = (currentPlayerPos - prevPlayerPos).normalized;
	posVector = (frontVector == Vector3.zero) ? posVector : frontVector;
	Vector3 targetPos = currentPlayerPos + scale * posVector;
	targetPos.y = targetPos.y + 0.5f;
	this.transform.position = Vector3.Lerp (
        this.transform.position,
        targetPos, 
        cameraSpeed * Time.deltaTime
    );
	this.transform.LookAt (player.transform.position);
	prevPlayerPos = player.transform.position;
}