In Jain Dharma, watching 18+ content is not treated lightly, because it increases kāma-rāga and vishaya-āsakti and strengthens passions like lust, attachment, and delusion.

For a layperson (gṛhastha), the needed purification is usually serious and sincere, but it is not the same as the strict renunciation expected from a monk. So the response should be:

• genuine repentance
• clear resolve not to repeat it
• pratikraman / prāyashchitta according to one’s tradition and capacity
• restraint in the future
• reducing sensual stimuli and strengthening self-control

So the answer is:

It requires a serious purification, not an ordinary casual one. But for a layperson, the emphasis is on true repentance and restraint, not extreme self-punishment.

If it happened once due to weakness, the purification can be lighter. If it became a repeated habit, then the purification and self-discipline should be much stronger.

In Jain spirit, the most important thing is: do not justify it, repent sincerely, and take a firm vow to reduce and छोड़ना it.