I believe that in this context, "Vorwurf" is used in the second sense of the word:
"Vorlage (3a); Thema, Gegenstand künstlerischer Bearbeitung
Herkunft
[...]
ursprünglich = das vor die Sinne Geworfene, das den Sinnen, dem Subjekt Gegenüberstehende
[...]
Beispiel
das Ereignis diente als Vorwurf für eine Novelle, zu seinem Roman"
http://www.duden.de/rechtschreibung/Vorwurf

You're talking about a "hokku," which is the "opening verse":
"the hokku served to begin a longer poem by establishing a season, often with a pair of seasonal images"
https://www.poetryfoundation.org/learn/glossary-terms/haiku-...

It's there to serve as the starting point for adding the other stanzas, Typically, it's the guest of hono(u)r (or the lead poet) who is asked to write (or recite) the hokku:
"It was traditional for the most honoured guest at the poetry-writing session to be invited to compose it, and he would be expected to offer praise to his host and/or deprecate himself (often symbolically), while superficially referring to current surroundings and season."
https://en.wikipedia.org/wiki/Hokku

"Note: As the invited guest, I had the honor of writing the hokku. I tried to keep with the tradition of referencing the host [...]. I also wanted to set the stage, explaining our different geographies."
https://haikuproject.wordpress.com/links/shared-water-a-reng...

"Its composition is considered an honour and would traditionally be reserved for the most practised poet present or offered as a mark of respect to a particularly worthy guest."
http://simplyhaiku.com/SHv2n1/renku/beginnings.html

There don't seem to be any negative connotations here:
"the hokku [...] will be the starting point [...] and should consequently be positive and forward-looking"
http://www.haikuspirit.org/renkuEN2.html

Cf
"The hokku is the head verse, the font from which the sequence springs. [...] The hokku is therefore the precursor to the later 'haiku'. Importantly, it is the only stanza in a renku sequence which may usefully be considered as 'like a haiku'."
http://simplyhaiku.com/SHv2n1/renku/beginnings.html

Interesting side note from Britannica:
"The hokku became known as the haiku late in the 19th century, when it was entirely divested of its original function of opening a sequence of verse, but today even the 17th-century hokku are usually called haiku."
https://www.britannica.com/art/Japanese-literature/Medieval-...

Cf
http://poetscollective.org/poetryforms/tag/van-gorder/page/5...

Considering that the hokku is the precursor to the haiku, I wouldn't use template, although Duden may suggest it; it's more like "source."

Your sentence reads: "Vorwurf des hokku."
This is a certain German grammar structure that you'd be better off translating into English by using something such as "called." The other word "lyrisch" only means "referring to poetry" here (not "lyric poetry").

Almost exactly the sentence you have, including "called" and "Tenor" as "set the tone":
"The first part of the poem, called hokku or 'starting verse,' frequently set the tone for the rest of the poem"

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Note added at 1 day18 hrs (2017-09-01 12:57:52 GMT) Post-grading
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Thanks for your kind words and glad to have helped!