So first of all, let's see what 5th house and 8th house represent -

5th house represents Creativity, Romance, Happiness, Hobbies, Children, Innovation, Sports, Movies, Stock Trading, Gambling and Betting, Risk Taking Ability, Education, Ancient Texts etc. 5th house lord should always be checked for career matters as it can indicate where our happiness lies in career.

8th house is house of secrecy, occult knowledge, longevity, transformation, death and re-birth, In laws family, joint wealth with spouse, serving other people needs etc.

Now, what does it mean to have 8th house lord sitting in 5th house?

It means the planet which rules/controls/owns the 8th house of your horoscope is sitting in the 5th house of horoscope.

Now, what is the impact of having 8th house lord sitting in 5th house?

Its generic interpretation is that this person will be highly interested in research related education. It means he will always choose those subjects to study which involves lots of research work. These people will be highly interested in any education related with Occult, Mysticism etc. It shows that few sudden events may impact their education. If it is a malefic planet in wrong dignity then it may block the education for some time. It can also show accidents while playing. Overall, it shows interests towards research related work & studies and sudden events impacting Education, Love Matters etc.

Now, results may be different due to aspect, conjunctions of other planets or the planet being Retrograde or Combust. Moreover, now we also need to check the strength of 5th house lord as 8th house lord is going in 5th house. So again, Overall Chart Reading is important.

So, let's see how different planets will behave differently as 8th house Lord in 5th house.

Sun - Suppose it is a Capricorn Ascendant chart and Sun rules the 8th house with Leo sign and sits in the 5th house in the sign of Taurus. This shows that person's education may be blocked for sometime due to certain sudden event. As Sun is in enemy sign, it shows the burnout of 5th house related things. This person may not be too much inclined towards Romance and all. With their children, they will behave in an authoritative way but at the same time this shows that person is interested in any work related to research & spying and that increases his wealth. His authoritative attitude disturbs love life and his relation with kids.

Moon - So it is Sagittarius Ascendant Chart and Moon rules the 8th house with Cancer sign and sits in 5th house in Aries. Here it shows that person is very headstrong related with his education. They treat education as if it is a war. Their Mother is like strict disciplinarian who keeps them on their toes in matters of education. They may be very good in sports too as Moon is in Mars ruled sign. This person will have a romantic side but he will try to dominate his partner.

Mars - Mars can be 8th house ruler through its two signs. So, let's take both one after the other.

Virgo Ascendant - So if it is Virgo Ascendant, Mars rules 8th & 3rd house and sits in 5th house in Capricorn sign, where it is exalted. This shows someone who is working for Govt in most chaotic situations and doing his job with perfection. So, it shows a Soldier or any other Govt Officer who works secretly for Govt and does all the spy work. This can also show someone who is in those kinds of sports where any sudden event can be fatal. But as Mars is exalted, they will come out as a winner in whatever they do, Again, in love matters, they may be dominant but here the arguments will be for good cause, no unnecessary fighting.

Aries Ascendant - Now if it is Aries Ascendant, Mars rules 8th & 1st house and sits in 5th house in Leo sign. A very similar position. We can see all the results detailed above here also. As Leo is sign of Govt, this is another position where person may be working with Govt. in the fields of research and chaotic work environment. Actually, with both positions of Mars, person may be in these chaotic and Army like work environments. He will show same attitude towards children and love partners. It shows good gains from Govt. and Authority.

Mercury - Mercury also can be 8th house ruler through its two signs. So, let's take both one after the other.

Scorpio Ascendant - If it is Scorpio Ascendant, Mercury rules 8th & 11th houses and sits in 5th house in Pisces, where it is debilitated. Mercury is probably the only planet which doesn't give any bad impact as not only it is a neutral planet but Pisces is also the most spiritual sign, which makes it quite a good type of debilitation. These people become highly imaginative with their Occult and Mystical knowledge. Then they use it in their writings. Mercury in Pisces always creates some of the best authors and here it is an author of Occult and Mysticism. They are very communicative with their children and love partners. Actually, Occult is the basic topic of discussion between them and their lovers.

Aquarius Ascendant - If it is Aquarius Ascendant, then Mercury rules 5th and 8th house and sits in 5th house in Gemini. This is even better situation than earlier one as Mercury is in own sign. Most of the results are quite similar. Additionally, this person will be very detailed and kind of perfectionist in his writing. As 8th house also represents Taxes, they can be in the field of Finance, Audit and Accountancy. Here, they can be good authors in these subjects. Highly communicative with Children and Love Partners.

Venus - Venus also can be 8th house ruler through its two signs. So, let's take both one after the other.

Libra Ascendant - If it is Libra Ascendant, Venus rules 8th & 1st house and sits in 5th house in Aquarius sign. This shows a natural love towards Occult and Mysticism. They may be working in some big organizations in matters related with research and finance. They are very much inclined towards love relations. Actually, it may be hard for them to be without love relation. Likewise, they love to have Children.

Pisces Ascendant - If it is Pisces Ascendant, Venus rules 3rd & 8th house and sits in 5th house in Cancer. This is all about love, emotions and care towards children and love partners. They are emotionally attached with all the Occult and Mysticism related stuff. They may be inclined to teach it to others which may bring them peace of mind. It looks like a position of a highly emotional person in matters of love relations and children. With both position of Venus, person is very creative and can make good name in the fields of art and cinema but here also the roles played by him will have intense effects of 8th house, means they will always go for dark and negative roles.

Jupiter - Jupiter also can be 8th house ruler through its two signs. So, let's take both one after the other.

Taurus Ascendant - If it is Taurus Ascendant, Jupiter rules 8th & 11th house and sits in 5th house in Virgo Sign. This shows a true teacher in field of occult and higher knowledge as planet of teaching is in the house of education. As Virgo is sign of details and perfection, these people will go to any length in their research to understand a concept of 8th house and then teach to their children. They are like guide or teacher to their love partners.

Leo Ascendant - If it is Leo Ascendant, Jupiter rules 5th & 8th house and sits in 5th house in Sagittarius. This is even better position as Jupiter is in its own sign. All the results given above will be multiplied here manifold. It shows a great teacher or a counselor is field of Occult, Mysticism, Higher Learning and Spirituality. You name a field of Occult and they will be master in that. A highly learned divine teacher. Like a Guru to their Children or Loved Ones.

Saturn - Saturn also can be 8th house ruler through its two signs.

In either sign (Capricorn/Aquarius) as 8th house lord, Saturn in 5th house (for Gemini/Cancer Ascendants respectively) shows a person who has a really serious outlook about studies and education. They treat education as their duty/responsibility and in such cases, fun part of life takes a back seat. It shows some real stressful relations which become burden in early 20s and break with time. Saturn here gives long duration relations and then it breaks, so the pain of separation is long lasting. They realize their creative side only in 30s. Saturn's 3rd aspect delays the marriage and hence child birth also gets delayed. Overall, it is a position of person who is seriously involved in studies and willing to leave fun part of life at least in 20s. This shows that sudden events disturbing the love life or education. Education may be delayed or blocked for some time. If Saturn is in Libra for Gemini Ascendant people, where it is exalted, then things may be 5% better, but nothing more than that. Fun filled life begins in 30s.

Rahu - If Rahu is 8th house Lord through its sign Aquarius, as it co-rules Aquarius along with Saturn, and sits in 5th house in Scorpio then 1st of all we need to make sure of Saturn's position as it is the main ruler. Rahu in Scorpio in 5th house will transform Rahu as Mars as Rahu changes its nature as per the lord of sign it is placed in. This shows some real troublesome relations coming to an abrupt end due to some sudden events. Person is obsessed for Occult and Mysticism. He is equally obsessed for being in love relation but it just doesn't work out for a long time. It shows some very unusual and weird relations. Online love affair can be seen from here. Unusual relation with Children. Person might have adopted a child or person might have adopted to all the new age techniques to have a child like Test Tube Baby or Surrogacy etc. Relationship with Children is equally troublesome and full of chaotic events.

Ketu - Likewise, If Ketu is 8th house Lord through its sign Scorpio, as it co-rules Scorpio along with Mars, and sits in 5th house in Leo then 1st of all we need to make sure of Mars' position as it is the main ruler. As Ketu isolates/separates a person from the things related to the house Ketu is sitting, here Creativity suffers. These people are either physically separated from being creative and attaining higher education, means they themselves won't be motivated to study any further after basic education. Likewise, they are not too much into sports, not even as a kid. Love relations would always end in painful breakups or cheating, so much so that later they won't even be inclined to any love relation. A benefic planet with Ketu or its aspect on Ketu/5th house or a running dasha of another planet can change this scenario completely.