"Soften" originated in late 14th-century Middle English as softenen or softnen, derived by adding the suffix -en (making/becoming) to the adjective soft.  It meant to mitigate, diminish sorrow, or make physically yielding, evolving from Old English roots that meant gentle, smooth, or agreeable.   Derived from soft (adj.), which comes from Old English sōfte ("gentle, mild, calm") and West Germanic samfti.  An earlier, now obsolete verb soft ("to make soft") existed in the early 13th century.  Originally meant to make something less harsh or to ease, transitioning into both transitive ("to soften something") and intransitive ("to become soft") meanings by the early 15th century. 

According to the Oxford English Dictionary (OED), the earliest known use of the verb soften is in the Middle English period (1150-1500) , with the earliest evidence dating from before 1382.  The verb appears before 1382 in the Early Version of the Wycliffite Bible.  Softening (adjective): Earliest evidence is before 1400 (found in Lanfranc's Science of Cirurgie).  Softener (noun): Earliest evidence is 1580.  Softened (adjective): Earliest evidence is around 1570.  The OED notes that an earlier verb form, soft (v.), existed from the early 13th century (c. 1225) but is now obsolete.  

Softened language—the use of quieter, more subtle, or introspective prose—is critical in storytelling to signal emotional transitions, acting as a bridge between high-stakes scenes and moments of reflection. It allows for a natural ebb and flow, preventing readers from experiencing emotional fatigue and enabling them to process significant developments. 

Key Aspects of Softened Transitions in Writing:
Pacing and Relief: While high-octane action attracts attention, quieter scenes (or "sequels") are essential for character development and integration. Softened, slower, or more reflective sentences act as a breathers, slowing the tempo after a crisis or intense emotional scene. Signaling Shifts in Tone: Transitions don't just bridge scenes; they signal to the reader how to interpret the emotional "color" of the story, ensuring that emotional shifts feel natural rather than jarring. 
Implied Emotion vs. Melodrama: Using "soft" language, such as focusing on a character’s internal quietude, rather than shouting or sobbing, often hits harder emotionally because it reflects human restraint. 
Bridging Techniques: Writers use softened language to link scenes by repeating a keyword, image, or concept from the end of one scene into the beginning of the next, creating a smooth segue that guides the reader through emotional changes. 
Focusing on Internal Landscape: When transitioning, turning away from intense outward action and towards sensory, internal details allows the reader to connect with the character's internal struggle, fostering a deeper sense of realism. 

Just the facts:

SOFTENED Synonyms: 139 Similar and Opposite Words | Merriam-Webster Thesaurus

SOFTEN Definition & Meaning - Merriam-Webster

SOFTEN Synonyms: 64 Similar and Opposite Words | Merriam-Webster Thesaurus