耳に忍ばせて

[zuotengdazuo]

「……ああ。本番、精霊が出現したら、君は小型のインカムを耳に忍ばせて、こちらの指示に従って対応してもらうことになる。一回、実戦を想定して訓練しておきたかったんだ」
「で、俺にどうしろと？」
「……とりあえず、岡峰珠恵教諭を口説いてきたまえ」

Hi. Could you please explain why the causative form of 忍ぶ is used here (bold part)? Since 忍ぶ can be a transitive verb, why isn’t 忍んで used here?

By the way, I‘m not sure if the underlined ことになる means “will end up” or “will be decided”. It seems either fits the context. What do you think this ことになる means or what it functions as here?
Thank you.

 

[SomeCallMeChris]

君は小型のインカムを耳に忍ばせて

When 忍ぶ is used as transitive verb, the object is the thing you are hiding from. eg. 人目を忍んで⇒hiding from sight

In this sentence, 小型のインカム is what's being hidden, 君 is doing the hiding, and 耳 is where it is hidden.
With 忍んで、君 is hiding from 小型のインカム in or behind 耳, which isn't at all what the author wants to say.　

if the underlined ことになる means “will end up” or “will be decided”

"decided", I think is better, or "determined", but I don't think the meaning of the expression fundamentally changes. The translation can change depending on how much we know about who was the cause and how much volition they had in it. However, I think ことになる just has a broad meaning here, not multiple meanings, and that there are many cases where multiple translations could be equally correct.

 

[Toritoribe]

To supplement to Chris-san's explanation, the transitive verb ～を忍ぶ means "to bear/endure/put up with ~ (恥を忍ぶ, 屈辱を忍ぶ)" or "to hide oneself from ~ (世を忍ぶ, 人目を忍ぶ)". Thus, in the causative form …に～を忍ばせる, に indicates the causee and を indicates the object "something the causee puts up with" or "something the causee hides themselves from".
cf.
敵を追う --> 部下に敵を追わせる
すしを食べる --> 子供にすしを食べさせる

In your example sentence, 耳 is not the causee, i.e., the one who is made to bear/hide, and インカム is not something the causee (= 耳) is made to bear or something the causee is made to hide themselves from.

Actually, 忍ばせる is not the causative form of 忍ぶ, but another transitive verb 忍ばせる "to carry/have something under cover/in concealment". を indicates the object, and に is the location where the object is hidden.

忍ばせる（しのばせる） の意味
１ 人に知られないよう隠し持つ。ひそかに入れておく。「懐に短刀を―・せる」

忍ばせる（しのばせる）の意味・使い方をわかりやすく解説 - goo国語辞書

忍ばせる（しのばせる）とは。意味や使い方、類語をわかりやすく解説。［動サ下一］［文］しのば・す［サ下二］１ 人に知られないよう隠し持つ。ひそかに入れておく。「懐に短刀を―・せる」２ 目立たないように物事を行う。「足音を―・せて近づく」 - goo国語辞書は30万8千件語以上を収録。政治・経済・医学・ITなど、最新用語の追加も定期的に行っています。

dictionary.goo.ne.jp

You can consider that 忍ばせる is almost always(or probably always) this intransitive verb, and is almost never (or probably never) used as the causative form of 忍ぶ. (I checked in a corpus, and confirmed that there's no example of the causative form.)

Needless to say, 忍ぶ doesn't have this meaning of 忍ばせる. That's why 忍んで can't be used there.

By the way, I‘m not sure if the underlined ことになる means “will end up” or “will be decided”. It seems either fits the context. What do you think this ことになる means or what it functions as here?

You can think ～てもらうことになる works as a soft request "you need to do".

 

[zuotengdazuo]

Thank you both. I didn’t realize the answer was as simple as that——忍ばせる is just another transitive verb.