Thinking of killing someone brutally, with enjoyment or strong intention, can bind very heavy paap karma, but it does not by itself create nikachit karma in the strict technical sense.

Let’s separate two things:

1. What actually binds karma?

In Jain dharma, karma is mainly bound by:

• Bhāva (inner state):

- violent intention, cruelty, hatred, revenge, etc. - enjoying the thought of someone’s pain or death.

• Kashāya (passions): anger, pride, deceit, greed.
• Yog (activity of mind, speech, body).

So, even only in thought, if you repeatedly and intensely imagine “I want to kill this person, and I enjoy that thought”, you are doing:

• Manodushcharitra (mental misconduct) – ill‑will, wishing harm.
• Saṅkalpi hiṁsā (planned / intentional violence) at the bhāva level.

This definitely binds strong ghāti karmas, can lead toward narak gati, and darkens the soul very deeply. You can read a simple explanation of how such intense, passion‑filled states bind strong karmas here: “Understanding the theory of Karma”

2. What is nikachit karma exactly?

In Jain karma theory:

• Nikachit bandha is a very special, technical type of bondage in which:

- the karma, once bound, - cannot be: - pre‑maturely brought to fruition, - transformed into another subtype, - increased or decreased in duration or intensity. - it will definitely give its exact result, at its fixed time; only udaya (suffering/experience) can finish it.

It is described as the tightest/most rigid bondage among karmas.

Scriptures describe nikachit karma mainly in the context of:

• long‑standing karmas from previous lives,
• that even very high tapas and punya cannot modify;
• they “must” be borne by Tirthankars, Kevalis, and others as part of their last residual karmas.

Important: Jain texts do not say in simple terms: “If you think of killing someone, you have surely bound nikachit karma.” They say: very intense, passion‑filled hiṁsā can become very strong karma, some of which may be of nikachit type, but only a Kevali can know exactly which bondages are nikachit.

So, to speak carefully and traditionally:

• Yes – brutal, repeated, intentional murderous thoughts bind very heavy paap and ghāti karmas, fit for narak.
• But – to label a specific person’s thought as “this is nikachit karma” is beyond ordinary knowledge; only an Omniscient can see that.

Both Digambar and Shvetāmbara agree on:

• Thought‑violence and intention are fully karmically effective.
• Stronger the passion and cruelty, stronger the bondage.
• Nikachit karma is a special fixed bondage, not something we can easily identify in day‑to‑day language.

3. What should you do if such thoughts arise?

From Jain dharma’s view, the urgent steps are:

1. Stop feeding the thought

Do not keep replaying or enjoying it. Drop it as soon as you notice.

1. Kshamā & Maitrī bhāvanā

- Consciously wish: “May this soul be happy, may I have friendship with all jivas.” - Remember: “I am responsible for my own karmas, not for punishing others.”

1. Pratikraman & Ālochana

- Admit inside: “This thought was wrong; Micchāmi Dukkadam.” - If you do daily pratikraman, include this in confession.

1. Reduce anger at its root

- Notice triggers, avoid situations that inflame hatred. - Practise silence and withdrawal when very angry.

1. Strengthen right vision (samyag‑darshan)

- Reflect: “That person, like me, is a soul covered by karma. Hurting them only deepens my own bondage.”

If you sincerely regret such thinking and work to change the inner state, the intensity and duration of the bound karmas can be reduced, even if some result must be borne. Jain karma doctrine clearly says that duration and intensity of most karmas (other than true nikachit) can be softened by right faith, right knowledge, and right conduct.

Summary:

• Mere thought of killing, if casual and immediately rejected, still binds paap but less.
• Enjoyed, repeated, revengeful thought of brutal killing binds very heavy paap and ghāti karmas and can lead toward narak.
• Whether that becomes nikachit karma in the strict sense is not something an ordinary person can judge; but it is serious enough that it should be stopped and repented immediately.