Let’s look at important things here –
Mercury - Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
Bharani – Bharani is nakshatra of death and re-birth, occult/hidden side of life and instabilities. This nakshatra is also connected with sexuality and attraction. As it is ruled by Venus, the significance of wealth, finance and creativity naturally comes to this nakshatra. For detailed information on Bharani Nakshatra, please check this link -https://www.astrosaxena.com/Bharanaksh .
Aries – As Bharani is part of Aries, Aries sign and its representations become important here. Aries is the 1st sign of zodiac belt, so it represents the things and energy of 1st house of horoscope like Self, Personality etc. Besides that, Aries is the sign of our individuality, our aggression, our actions, our competitive ability etc. Aries is ruled by Mars and it is consisted of 2 and half Nakshatras named Ashwini, Bharani and Krittika.
Mars – As Mars rules Aries, Mars’ position and dignity is important to know about the overall functioning of any planet in Aries.
Venus – Likewise as Venus rules Bharani, Venus's position and dignity is important to know about the overall functioning of any planet in Bharani.
Houses Involved – Also, we can’t afford to forget the houses involved as a planet can be ruling different houses and sitting in different house for every person as per ascendant and planet’s position. To know overall affect, we have to consider the houses involved as those areas of life are being impacted.
Interpretation of Mercury in Bharani Nakshatra – So, when Mercury is in Bharani Nakshatra, person's interests, hobbies, skills and communications are coming into domain of Bharani. It means that person will be interested in occult and dark side of life. Death & Re-birth and concepts of re-incarnation can be of high interests for them. There can be instability in relationship with siblings or with people related with the house which is ruled by Mercury. As Mercury is playful and Bharani is most closely related with Sex, they can also be very sexual by nature. At the same time, they can be good in financial matters. They should be careful while communicating and travelling as Mercury is in enemy sign of Mars. As Sex and Occult come together in Bharani, this nakshatra can be the closest to Tantra which is mix of both. Mercury in Bharani can also make someone Tantrik Practitioner. Overall, it can be an excellent position to become occult practitioner or for doing anything in field of research.
Role of Mars – Mars's placement is important to guide Mercury in right direction, being Aries's lord.
Role of Venus – Likewise, Venus's placement is important to guide Mercury in right direction, being Bharani's lord.
Other Factors – And of course, we need to consider conjunction, aspects, house lordship, house position and dashas etc to know the exact results of Mercury in Bharani. So, we always need to take a holistic view of chart rather than just 1 planetary position.
Conclusion – So, this is how I see Mercury in Bharani can work in a chart.
Hope this helps. Please post any comment or query you may have.