A Trickier Wordsquare Riddle

My favorite Wordsquare Riddles,
Inventing them, I can't resist.
But this, with four stanzas,
There might be a twist!

My first is perfectly happy,
Featured in a song of Coldplay's.
My second is roughly a hertz,
Back in Mozart days.

My third does not empty graves.
National, personal, why not?
My fourth determines your destiny.
Also, a task of the pilot.

A bit tricky? I apologize.
The clues are obvious as can be.
For the geniuses on this site
I bet they solve this easily!

Hint 1:

This is a Wordsquare, which is a crossword shaped like a square, and having same across and down clues. No other specification.

Hint 2:

For the first word, it is just a word in the lyrics, not the title. To make it easier: the song has the same birth date and month as Robert Baden Powell.

Hint 3:

I must admit that you must think laterally a bit, but I'm afraid that if I add the tag, the answers will go wild.

Hint 4:

Underestimating the last stanza will make you fail this puzzle.

The answer is a Wordsquare, but ...

... it is not a 4×4 square, despite there being four clues on the face of it. It turns out that the square is 5×5. Only four of the words are defined explicitly in the puzzle and all words are five letters long.

The first:

Bliss is a word in the lyrics of Something Just Like This: "Some superhero. Some fairytale bliss ..."

The second:

Lento is a musical instruction to play slowly and could be more or less one beat per minute. Thanks to MMAdams for the useful link and also for having the right idea about the Hertz clue.

The third:

To inter is to place a corpse in a grave at a funeral. And there are references to international and interpersonal.

The fourth:

Steer: a pilot steers an aircraft or it steers other ships into the harbour. And one is steered by one's destiny.

The final Wordsquare:

 B L I S S
L E N T O
I N T E R
S T E E R
S O R R •

But there's a twist:

It is clear by now that there is a fifth word:
Sorry: A bit tricky? I apologize.

Well, it's never too late to say that. :)

• 24/25!! At last someone realized that I didn't tell the size of the puzzle. One of the letters is wrong (obviously in the main diagonal) and once you get it, I will accept the answer. – William Nathanael Jul 4 '17 at 8:23

I have half an answer, but I'm not sure I'm on the right track here.

I started by looking at the second clue, it seemed the most straight forward:

My second is roughly a hertz,
Back in Mozart days.

Tempo in music is now measured in Beats Per Minute (BPM), but it didn't used to be. Back in "Mozart days" tempo was given using a word like "Largo" for slow, or "Presto" for fast, and these corresponded to different BPM. A Hertz is actually 60BPM, because a Hertz is one per second. The word I found that corresponded to about 60BPM was larghetto using this glossary.

That's way more than 4 letters! It is however,

4 syllables. IF we define syllables like the Japanese language does, where we split the word into consonant sounds and a paired vowel sound. This gives us la-r-ghe-tto.

Then I started looking at the first clue again:
My first is perfectly happy,
Featured in a song of Coldplay's.

Paradise fits for that, Pa-ra-di-se. But wait! That doesn't fit with the second clue, I hear you saying! Don't worry, if we were actually filling this into a grid with four Japanese characters on a side, la from larghetto and ra from Paradise would be the same symbol, so we don't have to worry about that.

The next two clues I'm not sure about, and I didn't want to waste time trying to force words to fit if it turns out I'm wrong about the twist on the puzzle in the first place, so I thought I'd post a partial answer first.

• Generally, you've been fooled by the main trick in this question. Refer back to the hint if you need too. For the second hint, yes, you are definitely on the right track, but the word itself is incorrect (I know there are some possibility on this one, so I suggest doing it last). One more thing: I don't understand Japanese! I guarantee it uses ABC alphabet. – William Nathanael Jul 4 '17 at 0:39